How we calculate

Your employer doesn't estimate your taxes: payroll software applies fixed, published withholding formulas. We implement those same formulas, one jurisdiction at a time, from the official documents listed below.

What we calculate

• Federal income tax withholding: IRS Publication 15-T (2026), percentage method for automated payroll systems, for both the 2020-and-later Form W-4 and the older allowance form.
• Social Security and Medicare: 6.2% up to the 2026 wage base, 1.45% on all wages, and 0.9% Additional Medicare on wages above $200,000.
• State income tax withholding: each state's own 2026 formula or tables, with its allowances, credits and supplemental (bonus) rate.
• State payroll contributions paid by employees: disability insurance, paid family and medical leave, long-term care and unemployment shares.
• Local income taxes: where cities, counties or school districts levy them, with resident and nonresident rates.
• Year-end estimate: your 2026 federal tax on the return, including the new deductions for tips, overtime, seniors and car-loan interest and the child tax credit, compared with what your checks withhold.

How we test

Tax agencies publish worked examples in their withholding guides. We turn every one into an automated test, 236 official examples in all, and the calculator must reproduce them to the cent (or within the rounding the agency itself documents) before any change goes live. Where an agency uses a wage-bracket table instead of a formula, we compute with the formula and note the difference of a few cents.

What we don't cover

Nonresident alien withholding, household employees, and employer-specific rounding are not modelled. Local taxes are included where listed on each state page. Results are estimates for information, not tax advice.

Sources by jurisdiction

Corrections

If a number here doesn't match your pay stub and you think we're wrong, write to contact@goodpaychecks.com with your state, pay frequency and the line that differs. We fix verified errors promptly and note them here.