Data sources & methodology
Last updated: July 2026
Freelance Money Tools runs entirely in your browser. The numbers you see come from a single maintained parameter file plus documented formulas — not from a black-box API. This page is the map: where each figure originates, what we assume by default, and where we intentionally simplify.
Default assumptions (most tax calculators)
- Single filer using the standard deduction
- No other W-2 wages, spouse income, or dependents modeled
- Federal tax only — no state or local income tax in totals
- No credits (EITC, child tax credit, premium tax credit, etc.)
- Estimates for planning — not a substitute for filing Form 1040
2026 snapshot (verify at a glance)
| Parameter | Value |
|---|---|
| Standard deduction (single) | $16,100 |
| Social Security wage base | $184,500 |
| Business mileage rate | 72.5¢/mile |
| Solo 401(k) employee deferral limit | $24,500 |
| HSA limit (self-only) | $4,400 |
| QBI phase-out begins (taxable income, single) | $201,750 |
2025 IRS & SSA sources
| Parameter | Official source |
|---|---|
| Tax brackets & standard deduction ($15,750 single) | IRS Rev. Proc. 2024-40 (+ OBBBA revisions) ↗ |
| Social Security wage base ($176,100) | SSA 2025 cost-of-living adjustment ↗ |
| Standard mileage rates | IRS Notice 2025-5 ↗ |
| Solo 401(k) limits | IRS Notice 2024-80 ↗ |
| SEP IRA limits | IRC §415 (annual inflation adjustment) ↗ |
| HSA contribution limits | IRS Rev. Proc. 2024-25 ↗ |
| QBI threshold & phase-out range | IRS Rev. Proc. 2024-40 ↗ |
2026 IRS & SSA sources
| Parameter | Official source |
|---|---|
| Tax brackets & standard deduction ($16,100 single) | IRS Rev. Proc. 2025-32 ↗ |
| Social Security wage base ($184,500) | SSA 2026 cost-of-living adjustment ↗ |
| Standard mileage rates | IRS Notice 2026-10 ↗ |
| Solo 401(k) limits | IR-2025-111 / IRS Notice 2025-67 ↗ |
| SEP IRA limits | IRC §415 (annual inflation adjustment) ↗ |
| HSA contribution limits | IRS Rev. Proc. 2025-19 ↗ |
| QBI threshold & phase-out range ($75,000 band) | IRS Rev. Proc. 2025-32 + OBBBA §70105 ↗ |
IRS publications we reference
- Schedule SE (Self-Employment Tax) ↗
- Publication 560 (Retirement Plans for Small Business) ↗
- Publication 535 (Business Expenses) ↗
- Estimated Taxes (Form 1040-ES) ↗
- Section 199A (QBI) overview ↗
Statutory constants (fixed in code)
| Rule | Value |
|---|---|
| Self-employment tax base | 92.35% of net Schedule C profit |
| Social Security (employee + employer halves) | 12.4% each (15.3% combined with Medicare on SE income) |
| Medicare | 2.9% + 0.9% additional Medicare above threshold |
| QBI deduction rate | 20% of qualified business income (with phase-out) |
| Home office simplified method | $5/sqft, max 300 sqft |
| HSA catch-up (55+) | $1,000 |
Known simplifications by tool
Single filer, standard deduction only, no other W-2 income, no credits, no AMT. Federal only — state income tax is not included.
Phase-out for single filers using taxable income before the QBI deduction. No W-2 wage limit, no SSTB vs non-SSTB distinction, no REIT/PTP income.
Employer share uses IRS Pub. 560 circular formula (25% of plan compensation after employee deferral). Assumes no other retirement plan coverage.
25% of adjusted net earnings, capped at annual IRS limit and compensation cap. No employee contributions.
Deduction capped at net self-employment profit; does not model premium tax credit interaction.
Planning models for comparison — not a full payroll or retirement plan illustration.
Business math only; no tax or legal advice on contracts or interest rates.
How we update & verify
- Each fall, when IRS and SSA publish inflation-adjusted figures, we add or update entries in
year-params.tswith notice numbers in comments. npm run buildruns parameter coverage checks and automated regression tests against hand-verified examples.- We spot-check 2–3 scenarios manually, update this page's date, and deploy.
- A scheduled reminder opens a GitHub issue each November so the next tax year's parameters are not missed.
Report an error
Wrong bracket, stale mileage rate, or a formula that does not match IRS Pub language? Email contact@freelancemoneytools.com. We treat data bugs as production incidents — especially on YMYL content.
Tax data last updated: July 2026. Sources & methodology
Found a wrong number? Email contact@freelancemoneytools.com — corrections ship fast. See also About and Terms.