How StubWhiz Calculates

Last updated: November 2026

Every calculator on StubWhiz works the way a payroll department does: it annualises one pay check, works out the year’s tax on that full-year picture, then divides the answer back into a single check. This page sets out the method, the official figures behind it, the assumptions built in, and how those figures are checked and kept current.

The method, step by step

  1. Annualise. Gross pay for one period is multiplied by the number of periods in the year — 26 for biweekly, 52 weekly, 24 semi-monthly, 12 monthly.
  2. Subtract pre-tax deductions. 401(k) contributions come off the amount used for federal income tax, but not the amount used for FICA. Other pre-tax deductions, such as health premiums paid through a cafeteria plan, come off both.
  3. Subtract the standard deduction for the filing status: $16,100 single, $32,200 married filing jointly, $24,150 head of household, for tax year 2026.
  4. Apply the federal brackets progressively — each slice of taxable income is taxed at its own rate, never the whole amount at the top rate.
  5. Add FICA. Social Security is 6.2% of wages up to the year’s wage base — $184,500 for 2026, so the most any employee pays is $11,439.00. Medicare is 1.45% of all wages, plus the 0.9% Additional Medicare Tax withholding on wages above $200,000 ($250,000 for married filing jointly).
  6. Estimate state tax with a simplified flat rate for the state chosen, then divide every annual figure back by the number of pay periods.

The figures and their sources

The federal brackets and standard deductions are the tax year 2026 amounts published in IRS Revenue Procedure 2025-32. The annualised percentage method follows IRS Publication 15-T, the publication employers use for withholding. The Social Security wage base is the Social Security Administration’s announced contribution and benefit base for 2026: $184,500. The bonus calculator’s flat method uses the IRS optional flat rate for supplemental wages, 22%.

Assumptions to know about

  • The standard deduction is the only deduction applied. Itemised deductions, tax credits and adjustments such as student-loan interest are not modelled, so a real check can differ.
  • Annualising assumes the check being calculated repeats all year. A one-off overtime week or a mid-year raise is withheld as if it were permanent, then trued up in the tax refund.
  • State tax is a simplified flat-rate estimate. It does not reproduce state brackets, state standard deductions or local taxes such as New York City tax — and nine states have no wage income tax at all.
  • The pay-stub example and the worked examples use the same formulas and the same 2026 figures as the live calculators.

Estimates, not payroll quotes

Results are careful estimates for education. Your employer’s payroll system applies your exact W-4, your state’s official withholding tables and your benefit elections, and can land a few dollars either side of our federal figure. Always verify important numbers against your own pay stub or IRS.gov.

How figures are checked and updated

Every figure is checked against the official IRS or SSA publication it comes from before it is published. Each autumn, when the IRS issues the new year’s brackets and the SSA announces the new wage base, the calculators and the bracket tables are updated together. If you spot a figure that does not match its source, tell us via the contact page — corrections are published, not hidden.

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