Methodology
The annualized model
Every calculation on this site starts with a full year. Annual gross pay is assembled first (for hourly work, the hourly rate times hours per week times 52), then the annual tax is calculated, and the annual figures are divided evenly across the pay frequency selected: 52 weekly, 26 biweekly, 24 semimonthly or 12 monthly paychecks.
This is an estimate of annual tax divided evenly, and it is labeled that way wherever results appear. Actual per-paycheck withholding is a different mechanism: an employer applies IRS Publication 15-T wage-bracket or percentage tables to each check, taking account of the employee W-4 and year-to-date wages. Real paychecks therefore differ somewhat from the per-check figures here, and the annual totals are the reliable figure for comparisons.
Federal income tax
Federal taxable wages are annual gross pay minus traditional 401(k) contributions, HSA contributions made through payroll, and pre-tax health insurance premiums. The 2026 standard deduction ($16,100 single, $32,200 married filing jointly, per IRS Revenue Procedure 2025-32) is subtracted, and the seven federal brackets for the filing status are applied to the remainder. Filing statuses offered are single and married filing jointly; other statuses are not in the verified data set and are not offered.
Social Security and Medicare (FICA)
FICA wages are calculated as their own step: gross pay minus HSA contributions and pre-tax health premiums. Traditional 401(k) contributions do not reduce FICA wages. Social Security tax is 6.2% of FICA wages up to the 2026 wage base of $184,500. Medicare tax is 1.45% of all FICA wages, plus an additional 0.9% on FICA wages above $200,000 for single filers or $250,000 for married couples filing jointly.
Because the model is annualized, the capped Social Security tax is spread evenly across the year. In an actual payroll, Social Security withholding stops mid-year once the wage base is passed, so late-year paychecks are larger than the annualized view suggests. The annual Social Security total is the same either way.
State income tax
State tax is calculated from the verified 2026 model for the selected state or the District of Columbia: the state standard deduction or allowance and the state brackets or formula, applied to pay after traditional 401(k) contributions. Six states use dedicated rules inside the model, including a federal-tax deduction in two states, an exemption phase-out in one, dedicated formulas in two, and one state where 401(k) contributions remain in state-taxable pay. Each state page describes its own model in plain language and cites its source.
The effect of HSA contributions and health premiums on state tax varies by state and is not modeled in this version. On the state side of the calculation, only the traditional 401(k) contribution is applied. The federal and FICA treatment of those contributions, described above, is modeled in full.
State parameters were verified against official state department of revenue sources and enacted state law on 2026-10-12. A small number of states have not cleared that verification; in the calculator they show federal tax and FICA with a pending-verification notice, and no state figure is presented for them.
Benchmark salaries
The worked example on each state page uses that state's benchmark salary: the average annual pay for the state from the U.S. Bureau of Labor Statistics Quarterly Census of Employment and Wages (QCEW) for 2024, rounded to the nearest $1,000. It is an average (mean) across all covered workers in the state, not a median, and it is used only to give the example a realistic, sourced salary figure for that state.
HSA contribution limits
The calculator validates an HSA contribution against gross pay only. The statutory HSA contribution limits for 2026, which depend on coverage tier, are not enforced by the calculator in this version, and a contribution entered above the statutory limit will be calculated as entered. The federal and FICA treatment described above applies to whatever amount is entered.
Local income tax
Local income taxes (city, county and school district taxes, and local earned income taxes) are not modeled jurisdiction by jurisdiction. The calculator accepts an annual local tax amount entered directly, calculated under the local rules that apply to the reader, and shows it as its own line in the paycheck breakdown and the annual summary.
Post-tax deductions and the zero floor
Roth 401(k) contributions and the generic other post-tax deduction reduce net pay only; they never change any tax line. Traditional and Roth 401(k) contributions together are validated against the 2026 employee elective-deferral limit of $24,500 (or gross pay, if lower). If the deductions and taxes entered exceed gross pay, net pay is floored at $0 and a notice is shown.
Rounding
Calculations run at full precision internally. Displayed amounts are rounded half-up to the nearest cent. Annual totals are computed from unrounded values and then rounded, so a displayed per-paycheck figure multiplied by the number of paychecks can differ from the displayed annual figure by a few cents of rounding.
What the model leaves out
All figures are before tax credits of any kind. The model does not cover bonuses, overtime rates or supplemental wages, itemized deductions, income other than wages and salaries, multi-state or part-year residence, or employer-side payroll taxes. Amounts from a specific employer can also differ because of benefit elections and withholding details that a general calculator cannot see. The estimate is a planning figure, not a prediction of a specific payroll outcome.