Data sources & methodology
Last updated: July 2026
TakeHomeBase runs entirely in your browser. The numbers you see come from maintained parameter files 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)
- Paycheck totals are estimates for planning — not exact employer withholding
- Federal income tax is annualized using current 2026 brackets and standard deductions
- FICA follows the current Social Security wage base and Medicare rates
- State estimates exclude local payroll taxes unless a jurisdiction is modeled separately
- Overtime defaults to weekly FLSA rules, with California daily rules called out explicitly
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 ↗ |
Primary sources we reference
- IRS 2026 inflation adjustments / Rev. Proc. 2025-32 ↗
- SSA contribution and benefit base ↗
- U.S. DOL overtime pay guidance ↗
- FLSA overtime advisor ↗
Core constants used in payroll estimates
| Rule | Value |
|---|---|
| Employee Social Security | 6.2% up to the annual wage base |
| Employee Medicare | 1.45% on all wages |
| Federal overtime floor | 1.5× after 40 hours in a workweek |
| California daily overtime | 1.5× after 8 hours/day, 2× after 12 hours/day |
Known simplifications by tool
Federal tax is annualized using 2026 brackets and standard deductions. It is not a replacement for the IRS withholding worksheet or Publication 15-T payroll tables.
State income tax uses the current estimate library and does not include every local tax, city tax, or employer-specific withholding variation.
Federal weekly overtime and California daily overtime are modeled. Meal-period premiums, shift differentials, union rules, and employer rounding policies are not modeled yet.
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@takehomebase.com. We treat data bugs as production incidents — especially on YMYL content.
Tax and payroll data last updated: July 2026. Sources & methodology
Found a wrong number? Email contact@takehomebase.com — corrections ship fast. See also About and Terms.