Data Sources & Citations
Last reviewed: May 17, 2026.
Every calculator and converter on FreeToolsToGo relies on publicly available formulas, government publications, or open standards. This page lists every external source we cite. All sources below are publicly accessible without a paywall or login. We do not use any subscription tax-research service, paid data provider, or proprietary aggregator.
For per-tool methodology detail, see the "How this calculation works" section on each tool page. The constants files in the codebase (src/lib/finance/constants/ and src/data/) include the same citations inline so future maintainers can verify each value against the source.
Federal income tax — IRS
| Source | Agency | Version | Used by |
|---|
| Rev. Proc. 2024-40 (2025 tax-year inflation adjustments) | IRS | 2025 tax year | Federal Income Tax, Capital Gains, SE Tax, Quarterly Estimated Tax, Paycheck |
| Publication 590-B Appendix B Table III — Uniform Lifetime Table | IRS | 2024 edition | RMD Calculator |
| Publication 936 — Home Mortgage Interest Deduction | IRS | 2024 edition | Mortgage, Refinance, HELOC |
| Publication 17 — Your Federal Income Tax | IRS | 2024 edition | Federal Income Tax, Quarterly Estimated Tax |
| Publication 15-T — Federal Income Tax Withholding | IRS | 2025 edition | Paycheck (W4 allowance value) |
| Notice 2024-80 — Retirement contribution limits 2025 | IRS | 2025 plan year | 401(k), Roth vs Traditional IRA, RMD |
| IRC § 1 (tax brackets) | US Code | as amended | Federal Income Tax, Capital Gains, Paycheck |
| IRC § 86 (Social Security taxation) | US Code | as amended | Federal Income Tax, Social Security Break-Even |
| IRC § 1401 / § 1402 (self-employment tax) | US Code | as amended | Self-Employment Tax, Quarterly Estimated Tax |
| IRC § 1411 (Net Investment Income Tax) | US Code | as amended | Capital Gains, Federal Income Tax |
| IRC § 6654 (estimated tax underpayment penalty) | US Code | as amended | Quarterly Estimated Tax |
| IRC § 3101 (FICA tax rates) | US Code | as amended | Paycheck, Self-Employment Tax |
| IRC § 415(c) / § 402(g) / § 414(v) (contribution limits) | US Code | as amended | 401(k) |
| Treas. Reg. § 1.401(a)(9)-9 (RMD divisors) | Treasury | current | RMD Calculator |
Mortgage / lending — CFPB
State sales tax — State DORs
State income tax — State DORs
Document / image standards
| Source | Agency | Version | Used by |
|---|
| ISO 32000-1 / Adobe PDF Reference 1.7 | ISO | 2008 | PDF Merge, PDF Splitter, PDF Compressor, PDF Editor, PDF Page Replacer, PDF Password Protect, PDF Unlocker, PDF OCR |
| pdf-lib (open-source PDF library) | MIT-licensed npm package | 1.17.x | All PDF tools |
| PDF.js (open-source PDF renderer) | Mozilla | 3.11.174 | PDF OCR, PDF Editor, PDF Page Replacer |
| Tesseract.js (open-source OCR engine) | Project Naptha | 4.x | PDF OCR, Image to Text |
| IS-Net segmentation model via @imgly/background-removal | img.ly (AGPL-3.0 library; IS-Net model) | 1.7.0 | Background Remover |
Web standards — IETF / W3C
License posture
All sources cited above are either:
- United States federal-government publications, which are works of the federal government and not subject to copyright under 17 U.S.C. § 105;
- State-government publications, where similar non-copyright status applies in most jurisdictions;
- Open standards (IETF RFCs, W3C recommendations, ISO standards where excerpted in interoperable form);
- Open-source software libraries we ship or load (pdf-lib, PDF.js, Tesseract.js, IS-Net) under their respective permissive licenses (MIT, Apache-2.0).
Reporting an error
If you believe a calculator on this site uses an outdated or incorrect value, email legal@freetoolstogo.com with the tool URL, the value you believe is wrong, and the authoritative source for the correct value. We review every such report.