6.2%
Social Security tax rate (employee share)
1.45%
Medicare tax rate (employee share)
$176,100
2025 Social Security wage base
0.9%
Additional Medicare tax above $200k
How federal withholding is calculated per paycheck
Payroll systems don't apply your tax bracket directly to a single paycheck — they annualize it first. Your gross pay for this period is multiplied by the number of pay periods in a year (52 for weekly, 26 for biweekly, 24 for semi-monthly, 12 for monthly) to estimate your annual income. The standard deduction for your filing status is subtracted, the federal tax brackets are applied to what's left, and the resulting annual tax is divided back down by the number of pay periods to get the withholding for this specific check.
This is why a bonus or one-time large paycheck often gets withheld at a much higher rate than your regular pay — the payroll system annualizes that spike as if you earned it every period all year, pushing more of your income into higher brackets for withholding purposes. Your actual tax liability is reconciled when you file, so an over-withheld bonus typically comes back as part of your refund.
FICA: Social Security and Medicare
- Social Security tax: 6.2% of gross wages up to the annual wage base ($176,100 in 2025) — earnings above this cap are not subject to Social Security tax
- Medicare tax: 1.45% of all gross wages, with no wage cap
- Additional Medicare tax: an extra 0.9% applies to wages above $200,000 (single) or $250,000 (married filing jointly) — withheld from the employee only, not matched by the employer
- Your employer matches the 6.2% and 1.45% portions dollar-for-dollar, though that match never appears on your paycheck
How pre-tax deductions change the math
Pre-tax deductions — 401(k) contributions, traditional health insurance premiums, HSA contributions — are subtracted from your gross pay before federal withholding is calculated, which lowers both your taxable income and your withholding. They do not reduce your Social Security or Medicare wages in most cases (health insurance is typically FICA-exempt too, but 401(k) contributions are still subject to FICA). A $200 per paycheck 401(k) contribution won't just build retirement savings — it also shrinks the paycheck's taxable base for federal withholding purposes.
ℹ️ This calculator shows federal withholding only
State and local income tax, if applicable, are on top of the federal, Social Security, and Medicare withholding shown here. States range from 0% (Texas, Florida, Washington, and others) to over 13% (California) — add your state's rate separately for a complete picture of your take-home pay.
Pay frequency changes your per-check number, not your annual total
Switching from monthly to biweekly pay doesn't change how much federal tax you owe for the year — it changes how that same annual amount is divided. Biweekly pay periods (26 per year) produce two months each year with three paychecks instead of two, which is why biweekly employees sometimes describe having 'extra' paychecks. Semi-monthly pay (24 periods, always the same two dates each month) spreads the same annual total more evenly but never produces a three-paycheck month.
Use the Paycheck Calculator to model any combination of gross pay, frequency, filing status, and pre-tax deductions to see exactly how much of a specific check reaches your account — and compare it against the US Income Tax Calculator to check your full annual picture, or the W-4 Withholding Calculator to see whether your current withholding is set correctly.