swaitsandClaude Opus 5.5
ad572ae89d
Stephen asked that specs come from recognized documents, not from anyone's memory. There is no single US bookkeeping bible; authority is layered, and this records it: - docs/spec/sources/: verbatim excerpts (whitespace normalized), each with URL, retrieval date, and the SHA-256 of the fetched file, of public-domain texts: Pacioli's 1494 treatise in Geijsbeek's 1914 translation (double entry, the trial balance, one money, write only forward, correct by opposite entry, close into capital); IRS Pub. 583, 538, 946, 15; the 1099-MISC/NEC instructions (2025 and 2026); 26 U.S.C. §6041, §6041A, §704; Treas. Reg. §1.263(a)-1(f) and -4(f); Notice 2015-82; Rev. Proc. 98-25; Form 1065 instructions; 17 U.S.C. §105. The excerpts were extracted by matching each passage against the fetched file, so none can contain text the source doesn't. - docs/spec/rules.md: the rule catalog, B-1 to B-22. Each rule says AUTHORITY, CONVENTION, or DECISION; cites its sources (FASB's Codification and Concepts Statement 8 and OpenStax quoted briefly, never copied: copyright and CC BY-NC-SA); and names the code that enforces it and the tests and proofs that check it. - Spec blocks in the code now carry SOURCE: lines into the catalog; AGENTS.md makes sourcing rule 0 of the formal-methods bar. Corrections the sources turned up: the de minimis limit is $500 in the regulation and $2,500 by Notice 2015-82 (both now cited); 1099 thresholds after 2026 are inflation-indexed, so the engine's flat $2,000 for 2027+ is an open question (B-19). Unverified ASC paragraphs (360-10-35-4, 340-10, 230-10-45-10, 606-10-55-37B, 210) are listed in docs/spec/README.md until someone with a FASB basic-view login reads them. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX
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Accounting periods and methods
IRS Publication 538 (Rev. January 2022). Governs fiscal years, periods, and the consistency of method.
IRS Publication 538
Source: https://www.irs.gov/publications/p538
Retrieved: 2026-10-13
SHA-256 of the retrieved file (p538.txt): dfaf00c55253ef28c3311e6767230365b60e13c22c87a87bb6a6bcc41bd2fa06
Tax year
A tax year is an annual accounting period for keeping records and reporting income and expenses.
Calendar year
A calendar year is 12 consecutive months beginning on January 1st and ending on December 31st.
Fiscal year
A fiscal year is 12 consecutive months ending on the last day of any month except December 31st.
Accounting methods
No single accounting method is required of all taxpayers. You must use a system that clearly reflects your income and expenses and you must maintain records that will enable you to file a correct return. In addition to your permanent accounting books, you must keep any other records necessary to support the entries on your books and tax returns. You must use the same accounting method from year to year.
Accrual method
Under an accrual method of accounting, you generally report income in the year it is earned and deduct or capitalize expenses in the year incurred.