Audit Finding
OpenWrong tax treatment
Multiple AI Tools
Federal Module -- Tax Table Application -- Wrong tax treatment
The Claim
Claude and ChatGPT correctly computed only 23–42% of full federal tax returns, with errors stemming from using percentage-based bracket calculations instead of IRS-mandated tax tables.The Error
The AI models applied a percentage-based marginal rate calculation to determine federal income tax liability instead of using the IRS-prescribed tax tables or tax computation worksheets. The correct method under IRS instructions for Form 1040 requires taxpayers to use the Tax Table (for taxable income under $100,000) or the Tax Computation Worksheet (for income $100,000 and above), not a direct percentage multiplication of income against bracket rates. This distinction produces materially different results and is a fundamental compliance requirement.
The Citation
IRC §1 (tax imposed); IRS Publication 505 (Tax Withholding and Estimated Tax); IRS Form 1040 Instructions — Tax Table and Tax Computation Worksheet (required method for computing tax liability) Column Tax TaxCalcBench benchmark (arXiv 2507.16126); ainvest.com (March 2026)
Business Impact
A small business owner relying on AI-computed federal tax liability could significantly underpay or overpay taxes, triggering IRS underpayment penalties under IRC §6654, interest charges, or an unexpected balance due at filing.
Verdict
KKATC Tax Response
Note
Source: ainvest.com March 2026, referencing Column Tax TaxCalcBench benchmark results. Claude Opus 4 scored 27.45% strict accuracy, ChatGPT scored lower. Primary benchmark data independently published by Column Tax on arXiv.KKATC Tax Prep and Consulting
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