diff --git a/crates/ledger-core/src/account.rs b/crates/ledger-core/src/account.rs
index 811728c..1ece5ea 100644
--- a/crates/ledger-core/src/account.rs
+++ b/crates/ledger-core/src/account.rs
@@ -6,6 +6,7 @@
 //! grouping on type, so getting this right is the whole game.
 
 use crate::{Currency, LedgerError};
+use rust_decimal::Decimal;
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 
@@ -72,6 +73,14 @@ pub struct Account {
     pub placeholder: bool,
     /// Day one: always the ledger's base currency (see R-5).
     pub currency: Currency,
+    /// Tax category key (see [`crate::tax`]), for revenue and expense
+    /// accounts.
+    #[serde(default)]
+    pub tax_category: Option<String>,
+    /// Percent deductible, overriding the category's default (e.g. 50 for
+    /// meals, 0 for penalties).
+    #[serde(default)]
+    pub deductible_percent: Option<Decimal>,
 }
 
 /// The registry of accounts. Owns id allocation for accounts it holds.
@@ -116,6 +125,22 @@ impl ChartOfAccounts {
         self.accounts.values()
     }
 
+    /// Set (or clear) an account's tax category and deductible percent.
+    pub fn set_tax(
+        &mut self,
+        id: AccountId,
+        category: Option<String>,
+        deductible_percent: Option<Decimal>,
+    ) -> Result<(), LedgerError> {
+        let a = self
+            .accounts
+            .get_mut(&id)
+            .ok_or(LedgerError::UnknownAccount(id))?;
+        a.tax_category = category;
+        a.deductible_percent = deductible_percent;
+        Ok(())
+    }
+
     /// Number of accounts in the chart.
     pub fn len(&self) -> usize {
         self.accounts.len()
diff --git a/crates/ledger-core/src/error.rs b/crates/ledger-core/src/error.rs
index 55a46ef..865c57d 100644
--- a/crates/ledger-core/src/error.rs
+++ b/crates/ledger-core/src/error.rs
@@ -132,6 +132,11 @@ pub enum LedgerError {
     #[error("purchase date plus useful life overflows the calendar")]
     AssetDateOverflow,
 
+    /// A tax category doesn't exist, doesn't fit the account, or has a bad
+    /// deductible percent.
+    #[error("invalid tax category: {0}")]
+    InvalidTaxCategory(String),
+
     /// Partnership members are misconfigured (shares, capital accounts).
     #[error("invalid members: {0}")]
     InvalidMembers(String),
diff --git a/crates/ledger-core/src/ledger.rs b/crates/ledger-core/src/ledger.rs
index 9a4a1a9..2921115 100644
--- a/crates/ledger-core/src/ledger.rs
+++ b/crates/ledger-core/src/ledger.rs
@@ -228,10 +228,55 @@ impl Ledger {
             parent,
             placeholder,
             currency: self.base_currency,
+            tax_category: None,
+            deductible_percent: None,
         })?;
         Ok(id)
     }
 
+    /// Set (or clear, with `None`) an account's tax category, and optionally
+    /// override the category's deductible percent (0 to 100). The category
+    /// must fit the account's type (see [`crate::tax::check_category`]).
+    pub fn set_account_tax(
+        &mut self,
+        account: AccountId,
+        category: Option<&str>,
+        deductible_percent: Option<Decimal>,
+    ) -> Result<(), LedgerError> {
+        self.check_account_tax(account, category, deductible_percent)?;
+        self.chart
+            .set_tax(account, category.map(str::to_string), deductible_percent)
+    }
+
+    /// The validation behind [`Self::set_account_tax`], for stores that
+    /// journal before mutating.
+    pub fn check_account_tax(
+        &self,
+        account: AccountId,
+        category: Option<&str>,
+        deductible_percent: Option<Decimal>,
+    ) -> Result<(), LedgerError> {
+        let a = self
+            .chart
+            .get(account)
+            .ok_or(LedgerError::UnknownAccount(account))?;
+        if let Some(key) = category {
+            crate::tax::check_category(key, a.account_type, None)?;
+        } else if deductible_percent.is_some() {
+            return Err(LedgerError::InvalidTaxCategory(
+                "a deductible percent needs a tax category".to_string(),
+            ));
+        }
+        if let Some(p) = deductible_percent
+            && (p < Decimal::ZERO || p > Decimal::from(100))
+        {
+            return Err(LedgerError::InvalidTaxCategory(format!(
+                "deductible percent {p} must be between 0 and 100"
+            )));
+        }
+        Ok(())
+    }
+
     /// Start a draft journal entry. Returns its id.
     ///
     /// This is the unchecked constructor: replay and internal callers
diff --git a/crates/ledger-core/src/lib.rs b/crates/ledger-core/src/lib.rs
index 8f32cc5..d6a831f 100644
--- a/crates/ledger-core/src/lib.rs
+++ b/crates/ledger-core/src/lib.rs
@@ -27,6 +27,7 @@ pub mod money;
 pub mod payroll;
 pub mod periods;
 pub mod reports;
+pub mod tax;
 
 pub use account::{Account, AccountId, AccountType, ChartOfAccounts, Side};
 pub use arap::{
@@ -51,3 +52,4 @@ pub use reports::{
     StatementLine, TrialBalance, TrialBalanceLine, balance_sheet_as_of, cash_flow, general_ledger,
     members_equity, profit_and_loss_for_period, trial_balance_as_of,
 };
+pub use tax::{TaxCategory, TaxForm, TaxKind, TaxSummary, TaxSummaryLine, tax_summary};
diff --git a/crates/ledger-core/src/tax.rs b/crates/ledger-core/src/tax.rs
new file mode 100644
index 0000000..eaf0824
--- /dev/null
+++ b/crates/ledger-core/src/tax.rs
@@ -0,0 +1,513 @@
+//! Tax categories: where each revenue and expense account lands on the
+//! business's income tax return, and how much of it is deductible.
+//!
+//! The books stay book-basis; this is the bridge a CPA (or tax software)
+//! walks across. Categories are *stable semantic keys* ("meals",
+//! "guaranteed_payments") rather than form line numbers, which move from
+//! year to year; each category says which returns it applies to. A
+//! deductible percentage (meals 50%, penalties 0%) turns book amounts into
+//! deductible amounts and surfaces the book-to-tax differences (Schedule
+//! M-1 items) instead of hiding them.
+//!
+//! Scope is deliberate, like fixed assets: no tax depreciation (MACRS,
+//! Section 179, bonus), no basis computations, no filing. Not tax advice.
+
+use crate::{AccountType, Ledger, LedgerError};
+use chrono::NaiveDate;
+use rust_decimal::Decimal;
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
+
+/// The federal income tax return a business files.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, PartialOrd, Ord)]
+#[serde(rename_all = "snake_case")]
+pub enum TaxForm {
+    /// Sole proprietorship or single-member LLC: Schedule C (Form 1040).
+    ScheduleC,
+    /// Partnership or multi-member LLC: Form 1065.
+    Form1065,
+    /// S corporation: Form 1120-S.
+    Form1120S,
+    /// C corporation: Form 1120.
+    Form1120,
+}
+
+impl TaxForm {
+    /// Every form.
+    pub const ALL: [TaxForm; 4] = [
+        TaxForm::ScheduleC,
+        TaxForm::Form1065,
+        TaxForm::Form1120S,
+        TaxForm::Form1120,
+    ];
+
+    /// "Form 1065", "Schedule C", ...
+    pub fn label(&self) -> &'static str {
+        match self {
+            TaxForm::ScheduleC => "Schedule C",
+            TaxForm::Form1065 => "Form 1065",
+            TaxForm::Form1120S => "Form 1120-S",
+            TaxForm::Form1120 => "Form 1120",
+        }
+    }
+
+    /// Parse "schedule_c", "1065", "1120s", "1120" (and their labels).
+    pub fn parse(s: &str) -> Option<TaxForm> {
+        let k: String = s
+            .to_lowercase()
+            .chars()
+            .filter(|c| c.is_ascii_alphanumeric())
+            .collect();
+        match k.as_str() {
+            "schedulec" | "c" => Some(TaxForm::ScheduleC),
+            "1065" | "form1065" => Some(TaxForm::Form1065),
+            "1120s" | "form1120s" => Some(TaxForm::Form1120S),
+            "1120" | "form1120" => Some(TaxForm::Form1120),
+            _ => None,
+        }
+    }
+}
+
+/// Where a category sits on the return.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum TaxKind {
+    /// Income (revenue accounts).
+    Income,
+    /// Cost of goods sold (expense accounts).
+    CostOfGoods,
+    /// A deduction (expense accounts).
+    Deduction,
+}
+
+/// One tax category.
+#[derive(Clone, Copy, Debug, Serialize)]
+pub struct TaxCategory {
+    /// Stable key, e.g. `"meals"`.
+    pub key: &'static str,
+    /// Human label, e.g. `"Meals"`.
+    pub label: &'static str,
+    /// Income, COGS, or deduction.
+    pub kind: TaxKind,
+    /// The returns it appears on.
+    pub forms: &'static [TaxForm],
+    /// Percent deductible by default (100 for most; meals 50).
+    pub default_deductible_percent: u32,
+    /// What to know about it, for the agent and the CPA.
+    pub note: &'static str,
+}
+
+const ALL: &[TaxForm] = &TaxForm::ALL;
+const CORPS: &[TaxForm] = &[TaxForm::Form1120S, TaxForm::Form1120];
+
+const fn cat(
+    key: &'static str,
+    label: &'static str,
+    kind: TaxKind,
+    forms: &'static [TaxForm],
+    pct: u32,
+    note: &'static str,
+) -> TaxCategory {
+    TaxCategory {
+        key,
+        label,
+        kind,
+        forms,
+        default_deductible_percent: pct,
+        note,
+    }
+}
+
+use TaxKind::{CostOfGoods, Deduction, Income};
+
+/// The catalog.
+pub const CATEGORIES: &[TaxCategory] = &[
+    cat(
+        "gross_receipts",
+        "Gross receipts or sales",
+        Income,
+        ALL,
+        100,
+        "Sales recorded gross (platform and processor fees are a separate deduction).",
+    ),
+    cat(
+        "returns_allowances",
+        "Returns and allowances",
+        Income,
+        ALL,
+        100,
+        "Refunds and allowances; reduces gross receipts.",
+    ),
+    cat(
+        "interest_income",
+        "Interest income",
+        Income,
+        ALL,
+        100,
+        "Pass-throughs report it separately to owners (portfolio income).",
+    ),
+    cat("other_income", "Other income", Income, ALL, 100, ""),
+    cat(
+        "cost_of_goods_sold",
+        "Cost of goods sold",
+        CostOfGoods,
+        ALL,
+        100,
+        "Inventory and direct costs of what was sold.",
+    ),
+    cat("advertising", "Advertising", Deduction, ALL, 100, ""),
+    cat(
+        "bad_debts",
+        "Bad debts",
+        Deduction,
+        ALL,
+        100,
+        "Only debts previously included in income (accrual basis).",
+    ),
+    cat(
+        "car_truck",
+        "Car and truck expenses",
+        Deduction,
+        ALL,
+        100,
+        "Actual costs or the standard mileage rate, not both.",
+    ),
+    cat(
+        "charitable_contributions",
+        "Charitable contributions",
+        Deduction,
+        ALL,
+        100,
+        "Separately stated to owners for partnerships and S corps; limited for C corps; not a Schedule C deduction.",
+    ),
+    cat(
+        "commissions_fees",
+        "Commissions and fees",
+        Deduction,
+        ALL,
+        100,
+        "Includes app store, marketplace, and payment processor fees.",
+    ),
+    cat(
+        "contract_labor",
+        "Contract labor",
+        Deduction,
+        ALL,
+        100,
+        "Payments to non-employees; see 1099 reporting.",
+    ),
+    cat(
+        "depreciation",
+        "Depreciation (book)",
+        Deduction,
+        ALL,
+        100,
+        "Book depreciation; tax depreciation (MACRS, Section 179, bonus) is computed separately by the CPA.",
+    ),
+    cat(
+        "employee_benefits",
+        "Employee benefit programs",
+        Deduction,
+        ALL,
+        100,
+        "",
+    ),
+    cat(
+        "guaranteed_payments",
+        "Guaranteed payments to partners",
+        Deduction,
+        &[TaxForm::Form1065],
+        100,
+        "Payments to partners for services or capital, regardless of profit; reported on each partner's K-1.",
+    ),
+    cat(
+        "insurance",
+        "Insurance (other than health)",
+        Deduction,
+        ALL,
+        100,
+        "",
+    ),
+    cat("interest_expense", "Interest", Deduction, ALL, 100, ""),
+    cat(
+        "legal_professional",
+        "Legal and professional services",
+        Deduction,
+        ALL,
+        100,
+        "Attorneys, accountants, consultants.",
+    ),
+    cat(
+        "meals",
+        "Meals",
+        Deduction,
+        ALL,
+        50,
+        "Generally 50% deductible; the other half is a book-to-tax difference.",
+    ),
+    cat("office_expense", "Office expense", Deduction, ALL, 100, ""),
+    cat(
+        "officer_compensation",
+        "Compensation of officers",
+        Deduction,
+        CORPS,
+        100,
+        "Wages paid to officer-shareholders through payroll.",
+    ),
+    cat(
+        "organization_startup",
+        "Organizational and start-up costs",
+        Deduction,
+        ALL,
+        100,
+        "Tax: up to $5,000 each deductible in the first year, the rest amortized over 180 months; the CPA computes it.",
+    ),
+    cat(
+        "pension_profit_sharing",
+        "Pension and profit-sharing plans",
+        Deduction,
+        ALL,
+        100,
+        "",
+    ),
+    cat(
+        "rent_equipment",
+        "Rent or lease: vehicles, machinery, equipment",
+        Deduction,
+        ALL,
+        100,
+        "",
+    ),
+    cat(
+        "rent_property",
+        "Rent or lease: other business property",
+        Deduction,
+        ALL,
+        100,
+        "",
+    ),
+    cat(
+        "repairs",
+        "Repairs and maintenance",
+        Deduction,
+        ALL,
+        100,
+        "",
+    ),
+    cat(
+        "salaries_wages",
+        "Salaries and wages",
+        Deduction,
+        ALL,
+        100,
+        "Employees (not owners of a partnership, whose pay is guaranteed payments).",
+    ),
+    cat("supplies", "Supplies", Deduction, ALL, 100, ""),
+    cat(
+        "taxes_licenses",
+        "Taxes and licenses",
+        Deduction,
+        ALL,
+        100,
+        "Payroll taxes, business licenses, state fees; not federal income tax.",
+    ),
+    cat(
+        "travel",
+        "Travel",
+        Deduction,
+        ALL,
+        100,
+        "Lodging and transportation away from home; meals go under Meals.",
+    ),
+    cat("utilities", "Utilities", Deduction, ALL, 100, ""),
+    cat(
+        "other_deductions",
+        "Other deductions",
+        Deduction,
+        ALL,
+        100,
+        "Software, subscriptions, bank fees, dues, and the rest; the CPA itemizes.",
+    ),
+    cat(
+        "nondeductible",
+        "Nondeductible expenses",
+        Deduction,
+        ALL,
+        0,
+        "Fines, penalties, political contributions, federal income tax: a book expense with no deduction.",
+    ),
+];
+
+/// Look up a category by key.
+pub fn category(key: &str) -> Option<&'static TaxCategory> {
+    CATEGORIES.iter().find(|c| c.key == key)
+}
+
+/// Check that `key` can tag an account of `account_type` and, when a form
+/// is known, that it appears on that form.
+pub fn check_category(
+    key: &str,
+    account_type: AccountType,
+    form: Option<TaxForm>,
+) -> Result<&'static TaxCategory, LedgerError> {
+    let c = category(key)
+        .ok_or_else(|| LedgerError::InvalidTaxCategory(format!("unknown tax category {key:?}")))?;
+    let fits = match c.kind {
+        TaxKind::Income => matches!(account_type, AccountType::Revenue | AccountType::Expense),
+        TaxKind::CostOfGoods | TaxKind::Deduction => account_type == AccountType::Expense,
+    };
+    if !fits {
+        return Err(LedgerError::InvalidTaxCategory(format!(
+            "{key} is for {} accounts, not {account_type:?}",
+            if c.kind == TaxKind::Income {
+                "revenue"
+            } else {
+                "expense"
+            }
+        )));
+    }
+    if let Some(f) = form
+        && !c.forms.contains(&f)
+    {
+        return Err(LedgerError::InvalidTaxCategory(format!(
+            "{key} does not appear on {}",
+            f.label()
+        )));
+    }
+    Ok(c)
+}
+
+/// One category's line on the tax summary.
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
+pub struct TaxSummaryLine {
+    /// Category key.
+    pub category: String,
+    /// Category label.
+    pub label: String,
+    /// The accounts that roll into it, `"CODE Name"`.
+    pub accounts: Vec<String>,
+    /// Book amount: revenue for income, expense for COGS and deductions.
+    pub book: Decimal,
+    /// Deductible (or taxable) amount after the deductible percentage.
+    pub tax: Decimal,
+}
+
+/// An account with P&L activity and no tax category.
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
+pub struct Uncategorized {
+    /// `"CODE Name"`.
+    pub account: String,
+    /// Revenue or Expense.
+    pub account_type: AccountType,
+    /// Book amount (normal side).
+    pub book: Decimal,
+}
+
+/// The tax summary for a period: book amounts by tax category, deductible
+/// amounts, and every account still needing a category.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct TaxSummary {
+    /// First date, inclusive.
+    pub start: NaiveDate,
+    /// Last date, inclusive.
+    pub end: NaiveDate,
+    /// The return, when known.
+    pub form: Option<TaxForm>,
+    /// Income categories.
+    pub income: Vec<TaxSummaryLine>,
+    /// Cost of goods sold.
+    pub cost_of_goods: Vec<TaxSummaryLine>,
+    /// Deductions.
+    pub deductions: Vec<TaxSummaryLine>,
+    /// P&L accounts with activity and no category.
+    pub uncategorized: Vec<Uncategorized>,
+}
+
+impl TaxSummary {
+    /// Book net income of the categorized accounts.
+    pub fn book_net(&self) -> Decimal {
+        sum(&self.income, |l| l.book)
+            - sum(&self.cost_of_goods, |l| l.book)
+            - sum(&self.deductions, |l| l.book)
+    }
+
+    /// Income less deductible amounts, before the CPA's other adjustments.
+    pub fn tax_net(&self) -> Decimal {
+        sum(&self.income, |l| l.tax)
+            - sum(&self.cost_of_goods, |l| l.tax)
+            - sum(&self.deductions, |l| l.tax)
+    }
+}
+
+fn sum(lines: &[TaxSummaryLine], f: fn(&TaxSummaryLine) -> Decimal) -> Decimal {
+    lines.iter().map(f).sum()
+}
+
+/// Build the tax summary for `[start, end]`, closing entries excluded (like
+/// the P&L). Deductible amounts round to the cent, half away from zero.
+pub fn tax_summary(
+    ledger: &Ledger,
+    start: NaiveDate,
+    end: NaiveDate,
+    form: Option<TaxForm>,
+) -> Result<TaxSummary, LedgerError> {
+    let pl = crate::reports::profit_and_loss_for_period(ledger, start, end, None)?;
+    let mut by_cat: BTreeMap<&'static str, TaxSummaryLine> = BTreeMap::new();
+    let mut uncategorized = Vec::new();
+    for line in pl.revenue.iter().chain(pl.expenses.iter()) {
+        let account = ledger.chart().find_by_code(&line.code).ok_or_else(|| {
+            LedgerError::InvalidTaxCategory(format!("unknown account {}", line.code))
+        })?;
+        let name = format!("{} {}", account.code, account.name);
+        let Some(c) = account.tax_category.as_deref().and_then(category) else {
+            uncategorized.push(Uncategorized {
+                account: name,
+                account_type: account.account_type,
+                book: line.amount,
+            });
+            continue;
+        };
+        // Income from an expense-type account (e.g. a contra) counts with
+        // its sign flipped, so returns reduce receipts.
+        let book = if c.kind == TaxKind::Income && account.account_type == AccountType::Expense {
+            -line.amount
+        } else {
+            line.amount
+        };
+        let pct = account
+            .deductible_percent
+            .unwrap_or_else(|| Decimal::from(c.default_deductible_percent));
+        let tax = (book * pct / Decimal::from(100))
+            .round_dp_with_strategy(2, rust_decimal::RoundingStrategy::MidpointAwayFromZero);
+        let entry = by_cat.entry(c.key).or_insert_with(|| TaxSummaryLine {
+            category: c.key.to_string(),
+            label: c.label.to_string(),
+            accounts: vec![],
+            book: Decimal::ZERO,
+            tax: Decimal::ZERO,
+        });
+        entry.accounts.push(name);
+        entry.book += book;
+        entry.tax += tax;
+    }
+    let mut out = TaxSummary {
+        start,
+        end,
+        form,
+        income: vec![],
+        cost_of_goods: vec![],
+        deductions: vec![],
+        uncategorized,
+    };
+    // Catalog order, so the summary reads like the return.
+    for c in CATEGORIES {
+        if let Some(line) = by_cat.remove(c.key) {
+            match c.kind {
+                TaxKind::Income => out.income.push(line),
+                TaxKind::CostOfGoods => out.cost_of_goods.push(line),
+                TaxKind::Deduction => out.deductions.push(line),
+            }
+        }
+    }
+    Ok(out)
+}
diff --git a/crates/ledger-core/tests/tax.rs b/crates/ledger-core/tests/tax.rs
new file mode 100644
index 0000000..fd788a6
--- /dev/null
+++ b/crates/ledger-core/tests/tax.rs
@@ -0,0 +1,230 @@
+//! Tax categories and the tax summary. Expected numbers computed by hand.
+//!
+//! The fixture: a partnership's first quarter.
+//!
+//! | account               | category              | % | book    | deductible |
+//! |-----------------------|-----------------------|---|---------|------------|
+//! | 4000 Sales            | gross_receipts        |   | 10,000  | 10,000     |
+//! | 4100 Refunds (exp.)   | returns_allowances    |   | 250     | (250)      |
+//! | 6000 Platform fees    | commissions_fees      |   | 1,500   | 1,500      |
+//! | 6100 Meals            | meals                 |50%| 333.33  | 166.67     |
+//! | 6200 Penalties        | nondeductible         | 0%| 40      | 0          |
+//! | 6300 Software         | other_deductions      |   | 600     | 600        |
+//! | 6400 Partner pay      | guaranteed_payments   |   | 2,000   | 2,000      |
+//! | 6500 Misc             | (none)                |   | 75      | uncategorized |
+
+use chrono::NaiveDate;
+use ledger_core::tax::{TaxForm, check_category, tax_summary};
+use ledger_core::{AccountType, Currency, Ledger, LedgerError, Money, Side};
+use rust_decimal::Decimal;
+use std::str::FromStr;
+
+fn d(m: u32, day: u32) -> NaiveDate {
+    NaiveDate::from_ymd_opt(2026, m, day).unwrap()
+}
+
+fn dec(s: &str) -> Decimal {
+    Decimal::from_str(s).unwrap()
+}
+
+fn books() -> Ledger {
+    let mut l = Ledger::new(Currency::USD);
+    let cash = l
+        .add_account("1000", "Cash", AccountType::Asset, None, false)
+        .unwrap();
+    let mut acct =
+        |code: &str, name: &str, t: AccountType, cat: Option<&str>, pct: Option<&str>| {
+            let id = l.add_account(code, name, t, None, false).unwrap();
+            if let Some(c) = cat {
+                l.set_account_tax(id, Some(c), pct.map(dec)).unwrap();
+            }
+            id
+        };
+    let sales = acct(
+        "4000",
+        "Sales",
+        AccountType::Revenue,
+        Some("gross_receipts"),
+        None,
+    );
+    let refunds = acct(
+        "4100",
+        "Refunds",
+        AccountType::Expense,
+        Some("returns_allowances"),
+        None,
+    );
+    let fees = acct(
+        "6000",
+        "Platform fees",
+        AccountType::Expense,
+        Some("commissions_fees"),
+        None,
+    );
+    let meals = acct("6100", "Meals", AccountType::Expense, Some("meals"), None);
+    let pen = acct(
+        "6200",
+        "Penalties",
+        AccountType::Expense,
+        Some("nondeductible"),
+        None,
+    );
+    let soft = acct(
+        "6300",
+        "Software",
+        AccountType::Expense,
+        Some("other_deductions"),
+        None,
+    );
+    let gp = acct(
+        "6400",
+        "Partner pay",
+        AccountType::Expense,
+        Some("guaranteed_payments"),
+        None,
+    );
+    let misc = acct("6500", "Misc", AccountType::Expense, None, None);
+    let mut post = |dr, cr, amt: &str| {
+        let e = l.create_entry(d(2, 1), "x");
+        l.add_line(e, dr, Side::Debit, Money::new(dec(amt), Currency::USD))
+            .unwrap();
+        l.add_line(e, cr, Side::Credit, Money::new(dec(amt), Currency::USD))
+            .unwrap();
+        l.post_entry(e).unwrap();
+    };
+    post(cash, sales, "10000");
+    for (a, amt) in [
+        (refunds, "250"),
+        (fees, "1500"),
+        (meals, "333.33"),
+        (pen, "40"),
+        (soft, "600"),
+        (gp, "2000"),
+        (misc, "75"),
+    ] {
+        post(a, cash, amt);
+    }
+    l
+}
+
+#[test]
+fn the_summary_groups_by_category_and_applies_deductible_percents() {
+    let l = books();
+    let ts = tax_summary(&l, d(1, 1), d(3, 31), Some(TaxForm::Form1065)).unwrap();
+    let rows = |lines: &[ledger_core::TaxSummaryLine]| -> Vec<(String, Decimal, Decimal)> {
+        lines
+            .iter()
+            .map(|l| (l.category.clone(), l.book, l.tax))
+            .collect()
+    };
+    // Refunds (an expense account) reduce receipts as negative income.
+    assert_eq!(
+        rows(&ts.income),
+        [
+            ("gross_receipts".into(), dec("10000"), dec("10000")),
+            ("returns_allowances".into(), dec("-250"), dec("-250")),
+        ]
+    );
+    // Catalog order; meals at 50% (333.33 → 166.665 → 166.67, half away
+    // from zero); penalties at 0%.
+    assert_eq!(
+        rows(&ts.deductions),
+        [
+            ("commissions_fees".into(), dec("1500"), dec("1500")),
+            ("guaranteed_payments".into(), dec("2000"), dec("2000")),
+            ("meals".into(), dec("333.33"), dec("166.67")),
+            ("other_deductions".into(), dec("600"), dec("600")),
+            ("nondeductible".into(), dec("40"), dec("0")),
+        ]
+    );
+    assert_eq!(ts.uncategorized.len(), 1);
+    assert_eq!(ts.uncategorized[0].account, "6500 Misc");
+    assert_eq!(ts.uncategorized[0].book, dec("75"));
+    // Book: 9,750 − 4,473.33 = 5,276.67. Tax: 9,750 − 4,266.67 = 5,483.33.
+    assert_eq!(ts.book_net(), dec("5276.67"));
+    assert_eq!(ts.tax_net(), dec("5483.33"));
+}
+
+#[test]
+fn an_override_beats_the_category_default() {
+    let mut l = books();
+    let meals = l.chart().find_by_code("6100").unwrap().id;
+    // A company party is 100% deductible: override the 50% default.
+    l.set_account_tax(meals, Some("meals"), Some(dec("100")))
+        .unwrap();
+    let ts = tax_summary(&l, d(1, 1), d(3, 31), None).unwrap();
+    let m = ts
+        .deductions
+        .iter()
+        .find(|x| x.category == "meals")
+        .unwrap();
+    assert_eq!(m.tax, dec("333.33"));
+}
+
+#[test]
+fn categories_must_fit_the_account_and_the_return() {
+    let mut l = books();
+    let sales = l.chart().find_by_code("4000").unwrap().id;
+    let meals = l.chart().find_by_code("6100").unwrap().id;
+    let bad = |r: Result<(), LedgerError>| matches!(r, Err(LedgerError::InvalidTaxCategory(_)));
+    assert!(
+        bad(l.set_account_tax(sales, Some("meals"), None)),
+        "deduction on revenue"
+    );
+    assert!(
+        bad(l.set_account_tax(meals, Some("no_such"), None)),
+        "unknown key"
+    );
+    assert!(
+        bad(l.set_account_tax(meals, Some("meals"), Some(dec("101")))),
+        "over 100%"
+    );
+    assert!(
+        bad(l.set_account_tax(meals, None, Some(dec("50")))),
+        "percent without category"
+    );
+    // Guaranteed payments exist only on a partnership return.
+    assert!(
+        check_category(
+            "guaranteed_payments",
+            AccountType::Expense,
+            Some(TaxForm::Form1065)
+        )
+        .is_ok()
+    );
+    assert!(
+        check_category(
+            "guaranteed_payments",
+            AccountType::Expense,
+            Some(TaxForm::ScheduleC)
+        )
+        .is_err()
+    );
+    assert!(
+        check_category(
+            "officer_compensation",
+            AccountType::Expense,
+            Some(TaxForm::Form1120S)
+        )
+        .is_ok()
+    );
+    // Clearing works.
+    l.set_account_tax(meals, None, None).unwrap();
+    assert!(l.chart().get(meals).unwrap().tax_category.is_none());
+}
+
+#[test]
+fn forms_parse_from_common_spellings() {
+    for (s, f) in [
+        ("schedule_c", TaxForm::ScheduleC),
+        ("Schedule C", TaxForm::ScheduleC),
+        ("1065", TaxForm::Form1065),
+        ("Form 1065", TaxForm::Form1065),
+        ("1120s", TaxForm::Form1120S),
+        ("1120-S", TaxForm::Form1120S),
+        ("1120", TaxForm::Form1120),
+    ] {
+        assert_eq!(TaxForm::parse(s), Some(f), "{s}");
+    }
+    assert_eq!(TaxForm::parse("990"), None);
+}
diff --git a/crates/ledger-import/src/chart_csv.rs b/crates/ledger-import/src/chart_csv.rs
index ee45bb1..1b201f6 100644
--- a/crates/ledger-import/src/chart_csv.rs
+++ b/crates/ledger-import/src/chart_csv.rs
@@ -24,16 +24,19 @@ pub struct ChartRow {
     pub account_type: String,
     /// Parent account code, if any.
     pub parent_code: Option<String>,
+    /// Optional fifth column: the tax category key (see
+    /// `ledger_core::tax`).
+    pub tax_category: Option<String>,
 }
 
 /// Parse errors.
 #[derive(Debug, Error, PartialEq)]
 pub enum ChartCsvError {
-    /// Wrong column count.
-    #[error("expected 4 columns (code,name,type,parent_code), found {0}")]
-    BadColumnCount(usize),
+    /// Wrong column count: (found, expected by the header).
+    #[error("expected {1} columns to match the header, found {0}")]
+    BadColumnCount(usize, usize),
     /// Missing or bad header.
-    #[error("bad header: expected code,name,type,parent_code")]
+    #[error("bad header: expected code,name,type,parent_code[,tax_category]")]
     BadHeader,
     /// Unknown account type.
     #[error("bad account type {0:?}: expected asset, liability, equity, revenue, or expense")]
@@ -48,9 +51,11 @@ pub enum ChartCsvError {
 pub fn parse_chart_csv(text: &str) -> Result<Vec<ChartRow>, ChartCsvError> {
     let mut reader = csv::ReaderBuilder::new()
         .has_headers(false)
+        .flexible(true)
         .trim(csv::Trim::All)
         .from_reader(text.as_bytes());
     let mut out = Vec::new();
+    let mut width = 4;
     for (idx, record) in reader.records().enumerate() {
         let record = record.map_err(|e| ChartCsvError::Csv(e.to_string()))?;
         let fields: Vec<&str> = record.iter().collect();
@@ -59,13 +64,17 @@ pub fn parse_chart_csv(text: &str) -> Result<Vec<ChartRow>, ChartCsvError> {
         }
         if idx == 0 {
             let lower: Vec<String> = fields.iter().map(|f| f.to_lowercase()).collect();
-            if lower != ["code", "name", "type", "parent_code"] {
+            width = if lower == ["code", "name", "type", "parent_code"] {
+                4
+            } else if lower == ["code", "name", "type", "parent_code", "tax_category"] {
+                5
+            } else {
                 return Err(ChartCsvError::BadHeader);
-            }
+            };
             continue;
         }
-        if fields.len() != 4 {
-            return Err(ChartCsvError::BadColumnCount(fields.len()));
+        if fields.len() != width {
+            return Err(ChartCsvError::BadColumnCount(fields.len(), width));
         }
         let account_type = fields[2].to_lowercase();
         match account_type.as_str() {
@@ -82,6 +91,11 @@ pub fn parse_chart_csv(text: &str) -> Result<Vec<ChartRow>, ChartCsvError> {
             } else {
                 Some(parent_code.to_string())
             },
+            tax_category: fields
+                .get(4)
+                .map(|s| s.trim())
+                .filter(|s| !s.is_empty())
+                .map(str::to_string),
         });
     }
     Ok(out)
@@ -101,6 +115,20 @@ mod tests {
         assert_eq!(rows[2].account_type, "revenue");
     }
 
+    #[test]
+    fn parses_optional_tax_category_column() {
+        let csv = "code,name,type,parent_code,tax_category\n4000,Sales,revenue,,gross_receipts\n1000,Cash,asset,,\n";
+        let rows = parse_chart_csv(csv).unwrap();
+        assert_eq!(rows[0].tax_category.as_deref(), Some("gross_receipts"));
+        assert_eq!(rows[1].tax_category, None);
+        // Rows must match the header's width.
+        let short = "code,name,type,parent_code,tax_category\n1000,Cash,asset,\n";
+        assert_eq!(
+            parse_chart_csv(short),
+            Err(ChartCsvError::BadColumnCount(4, 5))
+        );
+    }
+
     #[test]
     fn bad_type_rejected() {
         let csv = "code,name,type,parent_code\n1000,Cash,money,\n";
diff --git a/crates/ledger-import/src/report.rs b/crates/ledger-import/src/report.rs
index 513c592..7f056f5 100644
--- a/crates/ledger-import/src/report.rs
+++ b/crates/ledger-import/src/report.rs
@@ -400,6 +400,85 @@ pub fn members_equity(me: &MembersEquityStatement) -> Statement {
     )
 }
 
+/// Lay out the tax summary: book and tax amounts by tax category, the
+/// difference where they disagree (meals at 50%, penalties at 0%), and any
+/// account still needing a category.
+pub fn tax_summary(ts: &ledger_core::TaxSummary) -> Statement {
+    let diff = |b: Decimal, t: Decimal| if b == t { None } else { Some(b - t) };
+    let lines = |ls: &[ledger_core::TaxSummaryLine]| -> Vec<Row> {
+        ls.iter()
+            .map(|l| {
+                let codes: Vec<&str> = l
+                    .accounts
+                    .iter()
+                    .map(|a| a.split_whitespace().next().unwrap_or(""))
+                    .collect();
+                row(
+                    RowKind::Line,
+                    format!("{} ({})", l.label, codes.join(", ")),
+                    vec![Some(l.book), Some(l.tax), diff(l.book, l.tax)],
+                )
+            })
+            .collect()
+    };
+    let total = |kind, label: &str, ls: &[ledger_core::TaxSummaryLine]| {
+        let b: Decimal = ls.iter().map(|l| l.book).sum();
+        let t: Decimal = ls.iter().map(|l| l.tax).sum();
+        row(kind, label, vec![Some(b), Some(t), diff(b, t)])
+    };
+    let mut rows = vec![section("Income")];
+    rows.extend(lines(&ts.income));
+    rows.push(total(RowKind::Subtotal, "Total income", &ts.income));
+    if !ts.cost_of_goods.is_empty() {
+        rows.push(spacer());
+        rows.push(section("Cost of goods sold"));
+        rows.extend(lines(&ts.cost_of_goods));
+        rows.push(total(
+            RowKind::Subtotal,
+            "Total cost of goods sold",
+            &ts.cost_of_goods,
+        ));
+    }
+    rows.push(spacer());
+    rows.push(section("Deductions"));
+    rows.extend(lines(&ts.deductions));
+    rows.push(total(RowKind::Subtotal, "Total deductions", &ts.deductions));
+    rows.push(spacer());
+    rows.push(row(
+        RowKind::Total,
+        "Income less deductions",
+        vec![
+            Some(ts.book_net()),
+            Some(ts.tax_net()),
+            diff(ts.book_net(), ts.tax_net()),
+        ],
+    ));
+    if !ts.uncategorized.is_empty() {
+        rows.push(spacer());
+        rows.push(section("Not yet categorized"));
+        rows.push(subheading(
+            "Assign each a tax category (books.set_tax_category); not included above:",
+        ));
+        rows.extend(ts.uncategorized.iter().map(|u| {
+            row(
+                RowKind::Line,
+                u.account.clone(),
+                vec![Some(u.book), None, None],
+            )
+        }));
+    }
+    let title = match ts.form {
+        Some(f) => format!("Tax Summary ({} categories)", f.label()),
+        None => "Tax Summary".to_string(),
+    };
+    statement(
+        &title,
+        period_label(ts.start, ts.end),
+        &["Book", "Tax", "Difference"],
+        rows,
+    )
+}
+
 /// "October 11, 2026".
 pub fn long_date(d: NaiveDate) -> String {
     d.format("%B %-d, %Y").to_string()
diff --git a/crates/ledger-mcp/src/company.rs b/crates/ledger-mcp/src/company.rs
index bbafd8f..657c5e7 100644
--- a/crates/ledger-mcp/src/company.rs
+++ b/crates/ledger-mcp/src/company.rs
@@ -25,6 +25,9 @@ pub struct Company {
     pub members: Vec<Member>,
     /// "Accrual" or "Cash", for report footers. Default "Accrual".
     pub basis: String,
+    /// The income tax return the business files, if known: from
+    /// `tax_form`, else from `tax_classification`.
+    pub tax_form: Option<ledger_core::TaxForm>,
 }
 
 /// One member of a multi-member LLC.
@@ -45,6 +48,7 @@ impl Default for Company {
             fiscal_year_start: (1, 1),
             members: Vec::new(),
             basis: "Accrual".to_string(),
+            tax_form: None,
         }
     }
 }
@@ -87,6 +91,8 @@ struct BooksToml {
 struct CompanyToml {
     name: Option<String>,
     fiscal_year_start: Option<String>,
+    tax_form: Option<String>,
+    tax_classification: Option<String>,
     #[serde(default)]
     members: Vec<MemberToml>,
 }
@@ -104,6 +110,24 @@ struct BooksSection {
     accounting_basis: Option<String>,
 }
 
+/// The return a federal tax classification files: "partnership" → 1065,
+/// "s corporation" → 1120-S, "c corporation" → 1120, "sole proprietorship"
+/// or "disregarded entity" → Schedule C. Unrecognized: unknown.
+fn form_for_classification(c: &str) -> Option<ledger_core::TaxForm> {
+    let c = c.to_lowercase();
+    if c.contains("partnership") {
+        Some(ledger_core::TaxForm::Form1065)
+    } else if c.contains("s corp") || c.contains("s-corp") || c.contains("s_corp") {
+        Some(ledger_core::TaxForm::Form1120S)
+    } else if c.contains("c corp") || c.contains("c-corp") || c.contains("c_corp") {
+        Some(ledger_core::TaxForm::Form1120)
+    } else if c.contains("sole") || c.contains("disregarded") {
+        Some(ledger_core::TaxForm::ScheduleC)
+    } else {
+        None
+    }
+}
+
 /// Parse a share: "50%" or "0.5".
 fn parse_share(name: &str, s: &str) -> Result<Decimal, String> {
     let s = s.trim();
@@ -158,6 +182,14 @@ pub fn parse(text: &str) -> Result<BooksSettings, String> {
             return Err(format!("member shares sum to {total}, not 100%"));
         }
     }
+    company.tax_form =
+        match (&raw.company.tax_form, &raw.company.tax_classification) {
+            (Some(f), _) => Some(ledger_core::TaxForm::parse(f).ok_or_else(|| {
+                format!("tax_form {f:?}: expected schedule_c, 1065, 1120s, or 1120")
+            })?),
+            (None, Some(c)) => form_for_classification(c),
+            (None, None) => None,
+        };
     if let Some(basis) = raw.books.accounting_basis {
         company.basis = match basis.trim().to_lowercase().as_str() {
             "accrual" => "Accrual".to_string(),
@@ -282,6 +314,34 @@ mod tests {
         assert!(parse("[books]\naccounting_basis = \"modified\"\n").is_err());
     }
 
+    #[test]
+    fn tax_form_from_setting_or_classification() {
+        use ledger_core::TaxForm;
+        let form = |toml: &str| parse(toml).unwrap().company.tax_form;
+        assert_eq!(
+            form("[company]\ntax_form = \"1120s\"\n"),
+            Some(TaxForm::Form1120S)
+        );
+        assert_eq!(
+            form("[company]\ntax_classification = \"partnership\"\n"),
+            Some(TaxForm::Form1065)
+        );
+        assert_eq!(
+            form("[company]\ntax_classification = \"S corporation\"\n"),
+            Some(TaxForm::Form1120S)
+        );
+        assert_eq!(
+            form("[company]\ntax_classification = \"disregarded entity\"\n"),
+            Some(TaxForm::ScheduleC)
+        );
+        assert_eq!(
+            form("[company]\ntax_classification = \"partnership\"\ntax_form = \"1120\"\n"),
+            Some(TaxForm::Form1120)
+        );
+        assert_eq!(form(""), None);
+        assert!(parse("[company]\ntax_form = \"990\"\n").is_err());
+    }
+
     #[test]
     fn rejects_bad_settings() {
         assert!(parse("[company]\nfiscal_year_start = \"02-29\"\n").is_err());
diff --git a/crates/ledger-mcp/src/server.rs b/crates/ledger-mcp/src/server.rs
index 53da119..18e872e 100644
--- a/crates/ledger-mcp/src/server.rs
+++ b/crates/ledger-mcp/src/server.rs
@@ -512,6 +512,8 @@ impl BooksServer {
                 } else {
                     balance
                 }),
+                tax_category: a.tax_category.clone(),
+                deductible_percent: a.deductible_percent.map(|p| p.to_string()),
             });
         }
         Ok(Json(ChartOut {
@@ -1359,6 +1361,66 @@ impl BooksServer {
         Ok(Json(ImportBankCsvOut { imported, count }))
     }
 
+    #[tool(
+        name = "books.tax_categories",
+        description = "The tax categories an account can map to (where it lands on the income tax return), filtered to the business's return when wanderbooks.toml says which (tax_form or tax_classification). Each has a default deductible percent (meals 50, nondeductible 0) and guidance. Categories are stable keys, not form line numbers.",
+        annotations(read_only_hint = true)
+    )]
+    async fn tax_categories(&self) -> Result<Json<TaxCategoriesOut>, String> {
+        let form = self.company.tax_form;
+        let categories = ledger_core::tax::CATEGORIES
+            .iter()
+            .filter(|c| form.is_none_or(|f| c.forms.contains(&f)))
+            .map(|c| TaxCategoryOut {
+                key: c.key.to_string(),
+                label: c.label.to_string(),
+                kind: match c.kind {
+                    ledger_core::TaxKind::Income => "income",
+                    ledger_core::TaxKind::CostOfGoods => "cost_of_goods",
+                    ledger_core::TaxKind::Deduction => "deduction",
+                }
+                .to_string(),
+                default_deductible_percent: c.default_deductible_percent,
+                note: c.note.to_string(),
+            })
+            .collect();
+        Ok(Json(TaxCategoriesOut {
+            form: form.map(|f| f.label().to_string()),
+            categories,
+        }))
+    }
+
+    #[tool(
+        name = "books.set_tax_category",
+        description = "Map a revenue or expense account to a tax category (see books.tax_categories), optionally overriding its deductible percent; category null clears it. Drives the tax_summary report."
+    )]
+    async fn set_tax_category(
+        &self,
+        params: Parameters<SetTaxCategoryParams>,
+    ) -> Result<Json<SetTaxCategoryOut>, String> {
+        let p = params.0;
+        let mut store = self.lock()?;
+        let id = resolve_account(&store, &p.account)?;
+        let pct = match &p.deductible_percent {
+            Some(s) => Some(parse_amount(s)?),
+            None => None,
+        };
+        if let Some(cat) = &p.category {
+            let t = store
+                .ledger()
+                .chart()
+                .get(id)
+                .expect("resolved")
+                .account_type;
+            ledger_core::tax::check_category(cat, t, self.company.tax_form)
+                .map_err(|e| e.to_string())?;
+        }
+        store
+            .set_account_tax(id, p.category.as_deref(), pct)
+            .map_err(|e| e.to_string())?;
+        Ok(Json(SetTaxCategoryOut { ok: true }))
+    }
+
     #[tool(
         name = "books.import_chart_csv",
         description = "Import a chart of accounts from CSV (header: code,name,type,parent_code). Types: asset, liability, equity, revenue, expense. Parents must come before children. Fails on the first bad row; nothing is half-imported."
@@ -1371,10 +1433,26 @@ impl BooksServer {
         let rows = ledger_import::parse_chart_csv(&p.csv_text).map_err(|e| e.to_string())?;
         let mut store = self.lock()?;
         // Validate all rows first: nothing is half-imported.
+        let parse_type = |t: &str| match t {
+            "asset" => Ok(AccountType::Asset),
+            "liability" => Ok(AccountType::Liability),
+            "equity" => Ok(AccountType::Equity),
+            "revenue" => Ok(AccountType::Revenue),
+            "expense" => Ok(AccountType::Expense),
+            _ => Err(format!("bad account type: {t}")),
+        };
         for row in &rows {
             if store.ledger().chart().find_by_code(&row.code).is_some() {
                 return Err(format!("duplicate account code: {}", row.code));
             }
+            if let Some(cat) = &row.tax_category {
+                ledger_core::tax::check_category(
+                    cat,
+                    parse_type(&row.account_type)?,
+                    self.company.tax_form,
+                )
+                .map_err(|e| format!("{}: {e}", row.code))?;
+            }
         }
         let mut created = Vec::new();
         for row in rows {
@@ -1397,9 +1475,14 @@ impl BooksServer {
                 ),
                 None => None,
             };
-            store
+            let id = store
                 .add_account(&row.code, &row.name, account_type, parent, false)
                 .map_err(|e| e.to_string())?;
+            if let Some(cat) = &row.tax_category {
+                store
+                    .set_account_tax(id, Some(cat), None)
+                    .map_err(|e| e.to_string())?;
+            }
             created.push(row.code.clone());
         }
         let count = created.len();
@@ -1510,12 +1593,13 @@ impl BooksServer {
             "trial_balance" => self.export_trial_balance(&format, p.as_of.as_deref())?,
             "general_ledger" => self.export_general_ledger(&format, &p)?,
             "members_equity" => self.export_members_equity(&format, &p)?,
+            "tax_summary" => self.export_tax_summary(&format, &p)?,
             "profit_and_loss" => self.export_pnl(&format, p.start.as_deref(), p.end.as_deref())?,
             "balance_sheet" => self.export_balance_sheet(&format, p.as_of.as_deref())?,
             "cash_flow" => self.export_cash_flow(&format, &p)?,
             _ => {
                 return Err(format!(
-                    "bad report {:?}: expected general_journal, general_ledger, trial_balance, profit_and_loss, balance_sheet, cash_flow, or members_equity",
+                    "bad report {:?}: expected general_journal, general_ledger, trial_balance, profit_and_loss, balance_sheet, cash_flow, members_equity, or tax_summary",
                     p.report
                 ));
             }
@@ -1566,6 +1650,13 @@ impl BooksServer {
                 };
                 report::trial_balance(&reports::trial_balance_as_of(ledger, as_of), as_of)
             }
+            "tax_summary" => {
+                let (start, end) = statement_range(ledger, p.start.as_deref(), p.end.as_deref())?;
+                report::tax_summary(
+                    &ledger_core::tax_summary(ledger, start, end, self.company.tax_form)
+                        .map_err(|e| e.to_string())?,
+                )
+            }
             "members_equity" => {
                 let (start, end) = statement_range(ledger, p.start.as_deref(), p.end.as_deref())?;
                 let me =
@@ -1575,7 +1666,7 @@ impl BooksServer {
             }
             _ => {
                 return Err(format!(
-                    "bad report {report:?}: expected profit_and_loss, balance_sheet, cash_flow, trial_balance, or members_equity"
+                    "bad report {report:?}: expected profit_and_loss, balance_sheet, cash_flow, trial_balance, members_equity, or tax_summary"
                 ));
             }
         })
@@ -2684,6 +2775,13 @@ impl BooksServer {
                 .map_err(|e| e.to_string())?;
             statements.push(("members-equity", report::members_equity(&me)));
         }
+        statements.push((
+            "tax-summary",
+            report::tax_summary(
+                &ledger_core::tax_summary(ledger, fy, as_of, self.company.tax_form)
+                    .map_err(|e| e.to_string())?,
+            ),
+        ));
         statements.push((
             "trial-balance",
             report::trial_balance(&reports::trial_balance_as_of(ledger, as_of), as_of),
@@ -2878,6 +2976,60 @@ impl BooksServer {
         Ok(csv)
     }
 
+    fn export_tax_summary(&self, format: &str, p: &ExportParams) -> Result<String, String> {
+        let store = self.lock()?;
+        let ledger = store.ledger();
+        let (start, end) = statement_range(ledger, p.start.as_deref(), p.end.as_deref())?;
+        let ts = ledger_core::tax_summary(ledger, start, end, self.company.tax_form)
+            .map_err(|e| e.to_string())?;
+        let line = |l: &ledger_core::TaxSummaryLine| {
+            serde_json::json!({
+                "category": l.category, "label": l.label, "accounts": l.accounts,
+                "book": money(l.book), "tax": money(l.tax),
+            })
+        };
+        if format == "json" {
+            return serde_json::to_string_pretty(&serde_json::json!({
+                "start": ts.start.to_string(), "end": ts.end.to_string(),
+                "form": ts.form.map(|f| f.label()),
+                "income": ts.income.iter().map(line).collect::<Vec<_>>(),
+                "cost_of_goods": ts.cost_of_goods.iter().map(line).collect::<Vec<_>>(),
+                "deductions": ts.deductions.iter().map(line).collect::<Vec<_>>(),
+                "uncategorized": ts.uncategorized.iter().map(|u| serde_json::json!({
+                    "account": u.account, "book": money(u.book),
+                })).collect::<Vec<_>>(),
+                "book_net": money(ts.book_net()),
+                "tax_net": money(ts.tax_net()),
+            }))
+            .map_err(|e| e.to_string());
+        }
+        let mut csv = String::from("section,category,label,accounts,book,tax\n");
+        for (section, lines) in [
+            ("income", &ts.income),
+            ("cost_of_goods", &ts.cost_of_goods),
+            ("deductions", &ts.deductions),
+        ] {
+            for l in lines {
+                csv.push_str(&format!(
+                    "{section},{},{},{},{},{}\n",
+                    l.category,
+                    csv_escape(&l.label),
+                    csv_escape(&l.accounts.join("; ")),
+                    money(l.book),
+                    money(l.tax)
+                ));
+            }
+        }
+        for u in &ts.uncategorized {
+            csv.push_str(&format!(
+                "uncategorized,,,{},{},\n",
+                csv_escape(&u.account),
+                money(u.book)
+            ));
+        }
+        Ok(csv)
+    }
+
     fn export_members_equity(&self, format: &str, p: &ExportParams) -> Result<String, String> {
         let store = self.lock()?;
         let ledger = store.ledger();
diff --git a/crates/ledger-mcp/src/types.rs b/crates/ledger-mcp/src/types.rs
index ce8b823..b1fc7b6 100644
--- a/crates/ledger-mcp/src/types.rs
+++ b/crates/ledger-mcp/src/types.rs
@@ -48,6 +48,53 @@ pub struct ChartAccount {
     /// Current balance in the account's normal side, as a decimal string.
     /// Positive means a normal balance.
     pub balance: String,
+    /// Tax category key, if assigned.
+    pub tax_category: Option<String>,
+    /// Deductible percent override, if any.
+    pub deductible_percent: Option<String>,
+}
+
+/// Parameters for `books.set_tax_category`.
+#[derive(Debug, Deserialize, JsonSchema)]
+pub struct SetTaxCategoryParams {
+    /// Account code (or id).
+    pub account: String,
+    /// Tax category key from `books.tax_categories`; null clears it.
+    pub category: Option<String>,
+    /// Percent deductible, overriding the category default (decimal
+    /// string, 0 to 100), e.g. "100" for a fully deductible company party.
+    pub deductible_percent: Option<String>,
+}
+
+/// Result of `books.set_tax_category`.
+#[derive(Debug, Serialize, JsonSchema)]
+pub struct SetTaxCategoryOut {
+    /// True when set.
+    pub ok: bool,
+}
+
+/// One tax category.
+#[derive(Debug, Serialize, JsonSchema)]
+pub struct TaxCategoryOut {
+    /// Stable key.
+    pub key: String,
+    /// Label.
+    pub label: String,
+    /// "income", "cost_of_goods", or "deduction".
+    pub kind: String,
+    /// Percent deductible by default.
+    pub default_deductible_percent: u32,
+    /// Guidance.
+    pub note: String,
+}
+
+/// Result of `books.tax_categories`.
+#[derive(Debug, Serialize, JsonSchema)]
+pub struct TaxCategoriesOut {
+    /// The return the categories are filtered to, if configured.
+    pub form: Option<String>,
+    /// Categories.
+    pub categories: Vec<TaxCategoryOut>,
 }
 
 /// Result of `books.chart`.
diff --git a/crates/ledger-mcp/tests/mcp_stdio.rs b/crates/ledger-mcp/tests/mcp_stdio.rs
index 8b739b9..0dcc18b 100644
--- a/crates/ledger-mcp/tests/mcp_stdio.rs
+++ b/crates/ledger-mcp/tests/mcp_stdio.rs
@@ -139,7 +139,7 @@ fn mcp_end_to_end_over_stdio() {
     // Tool listing: 23 narrow tools, chart is read-only.
     let list = mcp.request("tools/list", json!({}));
     let tools = list["result"]["tools"].as_array().unwrap();
-    assert_eq!(tools.len(), 50, "expected 50 tools, got {}", tools.len());
+    assert_eq!(tools.len(), 52, "expected 52 tools, got {}", tools.len());
     let chart = tools.iter().find(|t| t["name"] == "books.chart").unwrap();
     assert_eq!(chart["annotations"]["readOnlyHint"], true);
     assert!(
@@ -882,6 +882,8 @@ fn mcp_statement_pdfs_and_cpa_package_over_stdio() {
             "general-ledger.xlsx",
             "profit-and-loss.pdf",
             "profit-and-loss.xlsx",
+            "tax-summary.pdf",
+            "tax-summary.xlsx",
             "trial-balance.pdf",
             "trial-balance.xlsx"
         ]
@@ -899,7 +901,7 @@ fn mcp_period_statements_over_stdio() {
     let toml = dir.join("wanderbooks.toml");
     std::fs::write(
         &toml,
-        "[company]\nname = \"Test Co\"\nfiscal_year_start = \"02-01\"\n[[company.members]]\nname = \"Owner\"\nshare = \"100%\"\ncapital_account = \"3000\"\n[books]\nreceipt_threshold = \"5.00\"\n",
+        "[company]\nname = \"Test Co\"\nfiscal_year_start = \"02-01\"\ntax_classification = \"partnership\"\n[[company.members]]\nname = \"Owner\"\nshare = \"100%\"\ncapital_account = \"3000\"\n[books]\nreceipt_threshold = \"5.00\"\n",
     )
     .unwrap();
     let data = dir.join("books-data");
@@ -1055,4 +1057,66 @@ fn mcp_period_statements_over_stdio() {
     assert_eq!(me["total"]["contributions"], "1000.00");
     assert_eq!(me["total"]["net_income"], "4.00");
     assert_eq!(me["total"]["ending"], "1004.00");
+
+    // Tax categories: filtered to the partnership return.
+    let cats = mcp.call("books.tax_categories", json!({}));
+    assert_eq!(cats["form"], "Form 1065");
+    let keys: Vec<&str> = cats["categories"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .map(|c| c["key"].as_str().unwrap())
+        .collect();
+    assert!(keys.contains(&"guaranteed_payments"));
+    assert!(
+        !keys.contains(&"officer_compensation"),
+        "a corporate category"
+    );
+    mcp.call(
+        "books.set_tax_category",
+        json!({"account": "4000", "category": "gross_receipts"}),
+    );
+    mcp.call(
+        "books.set_tax_category",
+        json!({"account": "6000", "category": "other_deductions"}),
+    );
+    let err = mcp.call_err(
+        "books.set_tax_category",
+        json!({"account": "4000", "category": "meals"}),
+    );
+    assert!(err.contains("expense"), "{err}");
+    let chart = mcp.call("books.chart", json!({}));
+    let sales = chart["accounts"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .find(|a| a["code"] == "4000")
+        .unwrap()
+        .clone();
+    assert_eq!(sales["tax_category"], "gross_receipts");
+    // Jan-Feb: 6.50 of sales, 3.00 of software, all categorized.
+    let ts = mcp.call(
+        "books.export",
+        json!({"format": "json", "report": "tax_summary", "start": "2026-01-01", "end": "2026-02-28"}),
+    );
+    let ts: serde_json::Value = serde_json::from_str(ts["content"].as_str().unwrap()).unwrap();
+    assert_eq!(ts["form"], "Form 1065");
+    assert_eq!(ts["income"][0]["book"], "6.50");
+    assert_eq!(ts["deductions"][0]["category"], "other_deductions");
+    assert_eq!(ts["uncategorized"].as_array().unwrap().len(), 0);
+    assert_eq!(ts["tax_net"], "3.50");
+    // A chart import validates categories before creating anything.
+    let err = mcp.call_err(
+        "books.import_chart_csv",
+        json!({"csv_text": "code,name,type,parent_code,tax_category\n6100,Meals,expense,,meals\n4100,Fees,revenue,,commissions_fees\n"}),
+    );
+    assert!(err.contains("4100"), "{err}");
+    let chart = mcp.call("books.chart", json!({}));
+    assert!(
+        chart["accounts"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .all(|a| a["code"] != "6100")
+    );
 }
diff --git a/crates/ledger-store/src/schema.rs b/crates/ledger-store/src/schema.rs
index f04b67c..69b803a 100644
--- a/crates/ledger-store/src/schema.rs
+++ b/crates/ledger-store/src/schema.rs
@@ -5,7 +5,7 @@
 //! is the current version.
 
 /// Current schema version.
-pub const SCHEMA_VERSION: u32 = 5;
+pub const SCHEMA_VERSION: u32 = 6;
 
 /// Migrations, in order. `MIGRATIONS[i]` migrates from version `i` to `i+1`.
 pub const MIGRATIONS: &[&str] = &[
@@ -179,5 +179,11 @@ ALTER TABLE lines ADD COLUMN class_id INTEGER;
 -- keeps the filing and the withdrawal.
 ALTER TABLE attachments ADD COLUMN withdrawn_at TEXT;
 ALTER TABLE attachments ADD COLUMN withdrawn_reason TEXT;
+"#,
+    r#"
+-- v6: tax categories on accounts (where each account lands on the return,
+-- and how much of it is deductible). Percent is TEXT, never REAL.
+ALTER TABLE accounts ADD COLUMN tax_category TEXT;
+ALTER TABLE accounts ADD COLUMN deductible_percent TEXT;
 "#,
 ];
diff --git a/crates/ledger-store/src/store.rs b/crates/ledger-store/src/store.rs
index 6ba3f92..4bc2d98 100644
--- a/crates/ledger-store/src/store.rs
+++ b/crates/ledger-store/src/store.rs
@@ -1789,6 +1789,30 @@ impl Store {
         Ok((id, sha, dedup))
     }
 
+    /// Set (or clear) an account's tax category and deductible percent.
+    /// Journaled as `account.tax_set`.
+    pub fn set_account_tax(
+        &mut self,
+        account: AccountId,
+        category: Option<&str>,
+        deductible_percent: Option<Decimal>,
+    ) -> Result<(), StoreError> {
+        self.ledger
+            .check_account_tax(account, category, deductible_percent)?;
+        let line = self.append_journal(
+            "account.tax_set",
+            json!({
+                "account_id": account,
+                "tax_category": category,
+                "deductible_percent": deductible_percent.map(|p| p.to_string()),
+            }),
+        )?;
+        self.ledger
+            .set_account_tax(account, category, deductible_percent)?;
+        apply_line_to_sqlite(&self.conn, &line)?;
+        Ok(())
+    }
+
     /// Link a previously filed (unlinked) receipt to an entry. A receipt
     /// already linked elsewhere must be unlinked first, so moving evidence
     /// off an entry always goes through [`Store::unlink_receipt`] and its
@@ -2712,6 +2736,19 @@ fn replay_line_into_ledger(
                 )));
             }
         }
+        "account.tax_set" => {
+            let pct = match p.get("deductible_percent").and_then(|v| v.as_str()) {
+                Some(s) => Some(s.parse().map_err(|_| {
+                    StoreError::JournalCorrupt("account.tax_set deductible_percent".into())
+                })?),
+                None => None,
+            };
+            ledger.set_account_tax(
+                get_u64(p, "account_id")?,
+                p.get("tax_category").and_then(|v| v.as_str()),
+                pct,
+            )?;
+        }
         "receipt.attached"
         | "receipt.linked"
         | "receipt.unlinked"
@@ -3074,6 +3111,16 @@ fn apply_line_to_sqlite(conn: &Connection, line: &JournalLine) -> Result<(), Sto
                 ],
             )?;
         }
+        "account.tax_set" => {
+            conn.execute(
+                "UPDATE accounts SET tax_category = ?, deductible_percent = ? WHERE id = ?",
+                params![
+                    p.get("tax_category").and_then(|v| v.as_str()),
+                    p.get("deductible_percent").and_then(|v| v.as_str()),
+                    get_u64(p, "account_id")? as i64,
+                ],
+            )?;
+        }
         "receipt.unlinked" => {
             conn.execute(
                 "UPDATE attachments SET entry_id = NULL WHERE id = ?",
diff --git a/docs/mcp-interface.md b/docs/mcp-interface.md
index 3c8c1ae..bc4aac7 100644
--- a/docs/mcp-interface.md
+++ b/docs/mcp-interface.md
@@ -218,6 +218,25 @@ posting.
     get "Members' equity" with members named; the balance sheet separates
     retained earnings from the fiscal year's net income (loss).
 
+## Tools — tax categories
+
+- `books.tax_categories {}` → `{ form?, categories: [{ key, label, kind,
+  default_deductible_percent, note }] }`: where an account can land on the
+  income tax return, filtered to the business's return when known
+  (`[company] tax_form`, or derived from `tax_classification`). Stable
+  semantic keys (`meals`, `guaranteed_payments`, `commissions_fees`, ...),
+  never form line numbers, which change by year.
+- `books.set_tax_category { account, category?, deductible_percent? }`:
+  map a revenue or expense account to a category (null clears),
+  optionally overriding its deductible percent. Journaled as
+  `account.tax_set`.
+- `books.export { report: "tax_summary" }`: book vs. tax amounts by
+  category, the difference where they disagree (meals 50%, penalties 0%),
+  and every P&L account still uncategorized. In the CPA package for the
+  fiscal year to date.
+- `books.import_chart_csv` accepts an optional fifth `tax_category` column,
+  validated before anything is created.
+
 ## Tools — import
 
 - `books.import_bank_csv { csv_text, bank_account_code, default_offset_code,
diff --git a/docs/parity.md b/docs/parity.md
index 271baf3..cd600ef 100644
--- a/docs/parity.md
+++ b/docs/parity.md
@@ -24,6 +24,7 @@ No other statuses.
 | General ledger by account (running balance, split) | Reports → General Ledger | partial | hand-verified fixture, ties to trial balance; no golden file yet |
 | Trial balance as of a date | Reports → Trial Balance (as of) | partial | hand-verified fixture; no golden file yet |
 | Statement of changes in members' equity | Reports → Statement of Changes in Equity | partial | hand-verified two-member fixture incl. rounding and a close; no golden file yet |
+| Tax line mapping + tax summary | Accounts → Tax line mapping; Tax reports | partial | hand-verified fixture (50% meals, nondeductible, contra income); no golden file yet |
 | Reversing entries | Reverse transaction | done | linked via `reversal_of` |
 | Canonical report snapshots (JSON) | — (our oracle format) | done | `reports::snapshot` |
 | Fixed-asset register + straight-line depreciation | Fixed Asset register | done | `assets.rs`; golden-covered schedule; idempotent runs; disposal with gain/loss |
diff --git a/docs/requirements.md b/docs/requirements.md
index c2f63d6..f143888 100644
--- a/docs/requirements.md
+++ b/docs/requirements.md
@@ -65,6 +65,14 @@ requirement conflict, the requirement wins.
   to the cent, the last member absorbing rounding, so every row's total is
   exact. Any equity change the roll-forward doesn't explain is shown as
   "other", never hidden.
+- **R-9d — Tax categories.** Revenue and expense accounts map to stable
+  tax categories (`ledger_core::tax::CATEGORIES`: key, label, income /
+  cost of goods / deduction, the returns it appears on — Schedule C, 1065,
+  1120-S, 1120 — default deductible percent, guidance), with an optional
+  per-account deductible percent. `tax_summary(start, end, form)` groups
+  the P&L by category with book and deductible amounts and lists
+  uncategorized accounts. Book basis only: no tax depreciation, basis, or
+  filing; not tax advice.
 - **R-10 — Canonical snapshots.** `reports::snapshot()` renders the three
   core reports as deterministic JSON (decimal strings, sorted lines, fixed
   keys). Two engines fed the same books must produce identical output. This
diff --git a/plan/STATUS.md b/plan/STATUS.md
index 3344c39..6eefdf5 100644
--- a/plan/STATUS.md
+++ b/plan/STATUS.md
@@ -214,4 +214,11 @@ interface is MCP, not a cloned GUI. The first storage + MCP slice is done
   accounts carry allocated earnings; the members'-equity statement treats
   those closes as income, not contributions, and the balance sheet shows
   only unallocated earnings. Replay now checks closing lines, not just ids.
+- 2026-10-11: Tax categories (Stephen: wanderbooks is a general MCP-first
+  accounting application, so features ship for every small business, not
+  when Wanderland needs them). Accounts map to stable categories rather than
+  form line numbers; each category knows its returns and default
+  deductible percent; the tax summary shows book vs. tax by category and
+  every uncategorized account. tax_form comes from config or the tax
+  classification. Schema v6.