Every computation in the OpenTax rules engine maps to an authoritative IRS source. The table below shows which publications, revenue procedures, and IRC sections govern each category of calculations, along with the source files you can audit on GitHub.
| Category | IRS Sources Cited | Engine Files |
|---|---|---|
| Filing status & standard deduction |
Rev. Proc. 2024-40 §3.01 (standard deduction amounts) Publication 501 (dependents, standard deduction, filing info) One Big Beautiful Bill Act (OBBBA) §70102 (2025 increase) |
constants.ts form1040.ts |
| Tax brackets & rates |
Rev. Proc. 2024-40 §3 (rate tables) 2025 Form 1040 Instructions (Tax Computation Worksheet) |
taxComputation.ts constants.ts |
| Child Tax Credit |
IRC §24 (credit amount, qualifying child definition) Publication 972 (Child Tax Credit worksheet) OBBBA §70101 (2025 increase to $2,200) |
childTaxCredit.ts |
| Earned Income Credit |
IRC §32 (earned income credit rules) Publication 596 (EITC eligibility & worksheet) Rev. Proc. 2024-40 §3.10 (2025 thresholds) |
earnedIncomeCredit.ts |
| Capital gains & losses |
IRC §1(h) (capital gains rate structure) Publication 550 (investment income & expenses) 2025 Schedule D & Form 8949 Instructions |
scheduleD.ts form8949.ts |
| Wash sale rules |
IRC §1091 (loss disallowance on substantially identical securities) Publication 550, Chapter 4 (wash sale guidance) |
washSale.ts |
| Itemized deductions |
IRC §63 (taxable income defined),
IRC §170 (charitable),
IRC §213 (medical) Publication 502 (medical expenses), Publication 526 (charitable contributions) 2025 Schedule A Instructions; OBBBA §§ (SALT cap adjustments) |
scheduleA.ts |
| HSA deductions |
IRC §223 (HSA eligibility, limits, distributions) Publication 969 (HSA and HDHP guide) Rev. Proc. 2024-25 (2025 HSA contribution limits) |
hsaDeduction.ts |
| Alternative Minimum Tax (AMT) |
IRC §§55–59 (AMT rules & exemptions) 2025 Form 6251 Instructions (computation worksheet) |
amt.ts |
| Education credits |
IRC §25A (AOTC & Lifetime Learning Credit) Publication 970 (tax benefits for education) 2025 Form 8863 Instructions |
educationCredit.ts |
| Saver's Credit |
IRC §25B (retirement savings contribution credit) 2025 Form 8880 Instructions |
saversCredit.ts |
| Dependent care credit |
IRC §21 (expenses for household and dependent care services) 2025 Form 2441 Instructions |
dependentCareCredit.ts |
| Energy credits |
IRC §25C (energy-efficient home improvement credit) IRC §25D (residential clean energy credit) 2025 Form 5695 Instructions |
energyCredit.ts |
| IRA deductions |
IRC §219 (retirement savings deduction) Publication 590-A (contributions to IRAs) |
iraDeduction.ts |
| Student loan interest |
IRC §221 (interest on education loans) Publication 970, Chapter 4 |
studentLoanDeduction.ts |
| RSU basis adjustment |
Publication 525 (taxable and nontaxable income) Form 8949 Instructions (Code B adjustment for incorrect basis) |
rsuAdjustment.ts |
| Interest & dividends | 2025 Schedule B Instructions (interest & ordinary dividends reporting threshold) | scheduleB.ts |
| Rental income |
IRC §469(i) (passive activity loss rules & $25K allowance) Publication 527 (residential rental property) 2025 Schedule E Instructions (Part I) |
scheduleE.ts |
| Additional income & adjustments | 2025 Schedule 1 Instructions (additional income and adjustments to income) | schedule1.ts |
| California 540 |
FTB Publication 1001 (supplemental guidelines to CA adjustments) CA Revenue & Taxation Code (tax rates, exemption credits, mental health tax) |
ca/form540.ts ca/constants.ts |
| Form 1040 (master return) |
2025 Form 1040 Instructions (line-by-line computation guide) QDCG Tax Worksheet (qualified dividends and capital gain tax) |
form1040.ts |
Next: see how these rules perform against real-world tax scenarios.