How we calculate

Last updated October 16, 2026 · Changelog

PayGuess estimates what an employer would withhold from one paycheck. The same tax engine runs the calculator, the worked examples on the state pages and our tests, so the numbers always agree. It runs entirely in your browser; your pay is never uploaded.

The approach

1. Gross pay from your hours, rate and overtime (including daily overtime in California, Alaska and Nevada), or your salary.
2. Pre-tax deductions such as 401(k), 403(b), 457(b), SIMPLE IRA, HSA, section 125 health and FSA, and dependent care FSA, applied with each state’s own rules (for example Pennsylvania taxes 401(k) money and New Jersey only excludes 401(k)).
3. Federal income tax with the IRS percentage method from Pub 15-T (2026), using your W-4 choices.
4. Social Security at 6.2% up to the 2026 wage base of $184,500, and Medicare at 1.45% plus 0.9% over $200,000 (IRS Pub 15).
5. State income tax with each state’s official 2026 withholding formula or tables, linked on every state page.
6. State payroll deductions (disability, paid leave, transit, unemployment) and local taxes (for example New York City, Philadelphia, Detroit, Ohio cities, Kentucky, Kansas City, St. Louis, Indiana and Maryland counties).

Sources

Every rate, bracket, deduction and wage cap comes from an official publication: the IRS, the Social Security Administration, each state’s revenue or labor department, and city tax offices. Each state page lists the ones it relies on with direct links. We check that every linked source still opens.

Testing

• 4,738 automated tests pass, built from the worked examples and wage-bracket tables printed in the official booklets. 12 known differences remain, each a few cents and each explained below.
• Federal: of 4,350 cells in the IRS wage-bracket tables, 4,339 match to the cent and the other 11 are within $1 (the tables use bracket midpoints).
• 121,181 cross-check cells compare our state results with independent sources: the official wage-bracket tables and the open-source PolicyEngine-US model.
• Browser tests open all 51 state pages, check that the calculator gives the same answer as the engine, and fail on any page error.

Known caveats

• District of Columbia: DC last published a full withholding booklet (FR-230) for 2018. We use its method with DC’s current tax rates, so treat DC as a close estimate.
• Mississippi: the official booklet contradicts itself for married couples who both work (its Table D uses $4,600 per spouse; its formula and text use $2,300). We follow the formula, so Table D employers may withhold less.
• Connecticut: employers may use the wage-bracket tables or the TPG-211 calculation rules. We use the rules; the tables can differ by up to about 50 cents a check.
• Small rounding differences (a cent or two) with a few booklet examples in New York, Yonkers, New Mexico, Kentucky and California, where the booklet rounds or uses a per-period table.
• We do not know your employer’s exact benefits setup, year-to-date totals or any special local taxes you did not enter. Your pay stub is the record.

Update schedule

We re-check federal and state sources when new withholding rules are published (most states publish in December and January, some mid-year), when a state announces a mid-year change, and at least once a quarter. Each state page shows the date it was last checked, and the changelog lists what changed.

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