Methodology & Tax Sources

Calculation approach

Federal withholding follows the annualized Percentage Method in IRS Publication 15-T for an automated payroll system. The default assumes a Form W-4 from 2020 or later, Step 2 unchecked, no Step 3 credits, and no Step 4 income or deduction adjustment. The calculator subtracts entered pre-tax amounts, calculates annual withholding, FICA, state withholding and supported employee payroll premiums, then divides annual totals by pay frequency.

State coverage

All 37 state pages in the directory plus the New York City resident page use a 2026 rule derived from the cited government source. Texas, Florida, Nevada, Tennessee, and Washington correctly show no broad individual state wage tax; Washington still includes covered employee payroll programs. New York City adds the resident table to New York State withholding. Ohio switches formulas based on whether the paycheck date falls before or after August 1, 2026.

State-specific inputs are exposed when the official method needs them. Arizona uses the elected A-4 percentage, Connecticut uses the CT-W4 code, and selected local-tax states accept an entered county, city, occupational, municipal, or school-district rate. An entered local percentage is a user-supplied input, not an address lookup.

Official sources

Review process

Calculation constants are transcribed from government publications and checked against worked examples or published rate descriptions. Changes are reviewed for filing status, annualization, paycheck rounding, wage caps, allowance treatment, midyear effective dates, and whether a charge belongs under income tax or a separate payroll program. Pages identify assumptions that the compact interface cannot capture.

Known limitations

This is an educational estimate, not payroll software, tax preparation, or legal advice. It does not fully model W-4 Step 2, dependent credits, multiple jobs, nonresident reciprocity, automatic address-to-local-tax lookup, employer-paid premium choices, special exemptions, tips, garnishments, year-to-date wage history, or every benefit’s FICA treatment. Massachusetts, Minnesota, and Oregon show the maximum permitted employee share of their applicable paid-leave program by default; an employer may pay more of that contribution. Georgia uses the formula effective May 11, 2026, so earlier 2026 checks may differ. New Jersey uses the published graduated rate schedule as a planning estimate rather than reproducing every NJ-W4 rate-selection path.

Update history

July 29, 2026: Added source-backed engines for the remaining directory locations, including CT-W4 code handling, Ohio’s midyear date switch, New York City resident withholding, official paycheck-rounding rules, and separately labeled employee payroll programs. Expanded the official source registry and made every location route use the shared calculator.

July 29, 2026: Added official South Carolina WH-1603F and North Carolina NC-30 annualized engines, expanded California and New Jersey guidance, and strengthened internal links between national, state, hourly, biweekly, tax-explainer, and methodology pages.

July 23, 2026: Replaced the generic state-rate approximation with eight source-backed state engines; changed federal calculations to IRS Publication 15-T; separated Washington and California employee payroll premiums; added national salary, biweekly, hourly, and paycheck-tax tools.

Related calculators

Start with the national paycheck calculator, calculate overtime with the hourly calculator, model 26 checks with the biweekly calculator, or review individual deductions in the paycheck tax guide.

Editorial responsibility

Paycheck Atlas independently maintains the calculation logic and explanatory content. Questions or suspected discrepancies can be sent to dev@evetrend.com. Include the page, inputs, expected result, and official source when reporting a calculation issue. Reports are reviewed before calculation constants are changed.