IRS Accuracy Verification
TCubed Tax's calculation engine is verified against IRS publications, official worksheets, ATS acceptance scenarios, and all 50 state tax codes. Every assertion traces to an IRS authority.
Methodology
Each test case is hand-calculated from IRS-published examples, worksheets, and revenue procedures. Expected values are documented inline with the specific IRS authority cited (e.g., Rev. Proc. 2024-40, IRC § 199A, Form 1040 Instructions).
The engine uses dual-path verification: tax table lookups and bracket-based worksheet calculations must agree to the penny. All functions are pure TypeScript with zero external dependencies, ensuring auditability.
Verification Suites
IRS Publication 17 Gold Standard
IRS Publication 17 (2025)
Standard deductions, itemized deductions (SALT cap, medical, charitable), self-employment tax, child tax credit, Additional Medicare Tax, NIIT, capital gains, and AMT verified against official IRS worked examples.
Publication 17 Walkthrough Verification
IRS Publication 17 Worksheets
Named IRS scenarios ($46K single, $120K MFJ, $55K HOH), Pub 550 investment income, Pub 590-A IRA phase-outs, Pub 915 Social Security taxation, and dual-path bracket verification.
Publication 596 & 915 Gold Standard
IRS Pub 596 (EITC), Pub 915 (Social Security)
EITC phase-in/max/phase-out for 0-3+ children, investment income ceiling, MFS disqualification. Social Security three-tier taxation, provisional income, tax-exempt interest interaction, MFS penalty, and tax torpedo effects.
IRS Tax Table Gold Standard
IRS Tax Tables & Rev. Proc. 2023-34, 2024-40
Official IRS tax table lookup for all filing statuses (Single, MFJ, MFS, HOH, QSS) for 2025 and 2026. Dual-path verification: table lookup vs. bracket worksheet must agree to the penny.
IRS Worksheet Verification
Form 1040 Instructions
Line-by-line replication of the Qualified Dividends & Capital Gains Worksheet, Child Tax Credit Worksheet, and EITC Worksheet from the Form 1040 instructions.
Form 1040 Integration Gold Standard
IRS Form 1040, Schedules 1-3, A-E, SE
Line-by-line Form 1040 mapping, schedule cross-references, field validation, and form-to-form consistency checks for the complete 1040 package.
IRS Credit Stacking Gold Standard
IRC § 24, 32, 25A, 21, 25B
Non-refundable vs. refundable credit ordering, credit stacking interactions, and tax liability limitation rules per IRS instructions.
ATS Acceptance Testing System
IRS MeF ATS Program
MeF XML schema validation, rejection error database (20+ codes), credential validation, and 8+ predefined ATS scenarios covering single filers, dual income, HOH, itemized, self-employment, capital gains, child tax credit, and retirement distributions.
IRS Rules & Compliance
Internal Revenue Code
IRC section compliance checks, structural integrity validation, and cross-formula consistency verification.
Gold Standard Full Returns
IRS Publication 17, Form 1040
End-to-end tax return computation for complete real-world scenarios verified against hand-calculated IRS results.
Formula Validator & Cross-Checks
IRC, IRS Forms
Mathematical identity verification, cross-formula consistency (AGI = income - adjustments, taxable = AGI - deductions), and dual-path computation checks.
QBI Deduction (Section 199A)
IRC § 199A, Form 8995
Simple sole prop below threshold, taxable income cap, SSTB phase-out, W-2 wage/UBIA limitation, multi-business aggregation, loss netting, and IRS Form 8995 examples.
State Tax Coverage — All 50 States
State Tax Codes, 2025-2026
All 50 states verified: 9 no-income-tax states, CA (9 brackets + mental health surtax), NY (9 brackets + NYC/Yonkers), and 39 graduated-bracket states. Includes 2025 and 2026 tax years.
Scenario Gauntlets (01-07)
IRS Publications, Real-World Returns
7 scenario suites: basic returns, self-employment, investments, credit interactions, edge cases, real-person composites, and regression gauntlet with boundary and stress tests.
What We Verify
Federal Tax
- •Tax brackets (all statuses, 2025-2026)
- •Standard & itemized deductions
- •SALT cap ($40K/2025 OBBB, with MAGI phaseout)
- •Self-employment tax (Schedule SE)
- •Capital gains (0/15/20% preferential rates)
- •Child Tax Credit with phaseout
- •EITC (0-3+ qualifying children)
- •Education credits (AOTC, LLC)
- •QBI deduction (IRC § 199A)
- •AMT, NIIT, Additional Medicare Tax
- •Social Security taxation (3-tier)
- •Retirement income distributions
Compliance & E-Filing
- •Form 1040 line-by-line mapping
- •Schedules 1-3, A-E, SE generation
- •Form 8995 (QBI) generation
- •MeF XML schema validation
- •IRS ATS acceptance scenarios
- •Rejection code database (20+ codes)
- •Cross-check formula consistency
- •Audit risk scoring
- •Integrity & completeness checks
- •Dual-path computation verification
- •Cryptographic proof chains
- •All 50 state tax calculations
Tests run on every commit via CI. Results reflect the latest passing build.