How the FICA Tax Calculator works
FICA — the Federal Insurance Contributions Act — is the payroll tax that funds Social Security and Medicare. It is separate from federal and state income tax and is calculated with its own flat rates rather than progressive brackets. This calculator applies the standard federal formula to your annual income, employment type, and filing status.
The formula
FICA has two core components, each with an employee/employer split for W-2 workers and a combined self-employment rate for the self-employed:
- Social Security tax: 6.2% of wages for employees (12.4% total for the self-employed), applied only up to the annual Social Security wage base. Earnings above the wage base owe no additional Social Security tax that year.
- Medicare tax: 1.45% of wages for employees (2.9% total for the self-employed), with no wage cap — every dollar of earned income is subject to Medicare tax.
- Additional Medicare Tax: an extra 0.9%, paid only by the employee or self-employed individual (never matched by an employer), on earnings above $200,000 (single or head of household), $250,000 (married filing jointly), or $125,000 (married filing separately). These thresholds are fixed by statute, not adjusted for inflation.
For the self-employed, the tax base is net earnings from self-employment, calculated as net profit × 92.35%. That 92.35% multiplier exists because the employer-equivalent half of self-employment tax is not itself subject to self-employment tax, mirroring how an employer's matching FICA contribution is never counted in an employee's own wages.
Worked example
An employee earning $75,000 in wages, filing single, with a $176,100 wage base: Social Security tax is $75,000 × 6.2% = $4,650 (well under the wage base, so the full amount is taxed). Medicare tax is $75,000 × 1.45% = $1,087.50. Income is below the $200,000 Additional Medicare Tax threshold, so that component is $0. Total FICA tax is $5,737.50, an effective rate of about 7.65% of wages.
A self-employed person with $75,000 in net profit first computes net earnings from self-employment: $75,000 × 92.35% = $69,262.50. Social Security tax is $69,262.50 × 12.4% = $8,588.55, and Medicare tax is $69,262.50 × 2.9% = $2,008.61, for a combined self-employment FICA tax of $10,597.16 — roughly 14.13% of net profit, since the full 15.3% combined rate applies to the smaller 92.35% base.
What the calculator assumes
The wage base field lets you match the calculator to the tax year you are estimating, since the Social Security Administration typically adjusts this figure each year for average wage growth. For self-employment, the calculator applies the Additional Medicare Tax threshold to self-employment earnings alone; a person with both wages and self-employment income in the same year should combine the two before comparing against the threshold, since the IRS applies it to total earned income, not each income source separately. The calculator does not include federal or state income tax, which are computed separately using progressive brackets and deductions.
Common mistakes
- Applying the 6.2%/12.4% Social Security rate to all income instead of stopping at the wage base — high earners overpay if the cap is ignored.
- Forgetting the 92.35% net-earnings adjustment for self-employment tax, which understates the base and overstates the tax if skipped.
- Assuming an employer matches the Additional Medicare Tax — it does not; only the extra 0.9% employee/self-employed share applies, with no employer match.
- Confusing FICA with total tax withholding — FICA is separate from, and in addition to, federal and state income tax.