How this instrument works
FICA is not one tax but two, bundled onto a single payroll line: Social Security at 6.2% and Medicare at 1.45%, each funding its own trust fund under a law passed in 1935 and expanded in 1965. The two halves behave completely differently once wages climb. Social Security withholding stops the moment wages cross the annual wage base — $168,600 in this calculator — because the program is built to replace a bounded share of pre-retirement earnings, not to charge income without limit. Medicare withholding keeps applying to every dollar, uncapped since Congress removed its own wage ceiling in 1994, because the hospital insurance fund it feeds was never built around a benefit tied to a wage cap.
A third piece, the Additional Medicare Tax, arrived with the Affordable Care Act in 2013: an extra 0.9% on wages above $200,000, withheld by the employer but never matched — the employer's own Medicare share stays flat at 1.45% no matter how high an employee's pay climbs. That $200,000 line is fixed in the statute rather than indexed to wage growth the way the Social Security wage base is, so a threshold that once caught only the highest earners pulls in more workers every year simply because average pay keeps rising while the line does not move.
This instrument computes the employee's half only — the amount actually withheld from a paycheck. An employer owes a matching 6.2% and 1.45% on the same wages, invisible on any pay stub but very real on a payroll register; someone self-employed pays both halves personally through the separate SECA tax, at close to double this rate. A worker who changes jobs mid-year can also see the Social Security cap applied twice, once per employer, and end up over-withheld — a mismatch this instrument does not correct, since it works from a single employer's wages.
- Enter the pay period or annual total into Gross wages, $ — the figure before any tax or benefit deduction.
- Read Social Security tax (6.2%, capped) — the instrument applies the rate only up to the $168,600 wage base.
- Read Medicare tax (1.45%, uncapped) — this applies to every dollar of Gross wages, $, with no ceiling.
- Watch Additional Medicare tax (0.9% above $200,000) switch on once Gross wages, $ crosses that threshold.
- Read Total FICA tax withheld for the sum of all three — the figure a pay stub's FICA line should match.
Worked example — an $80,000 salary
Set Gross wages, $ to 80,000. Social Security tax applies the full 6.2% because $80,000 sits well under the $168,600 wage base: 80,000 × 0.062 = $4,960.00 exactly, with nothing capped away. Medicare tax applies its flat 1.45% to the same $80,000 with no ceiling at all, giving $1,160.00.
Wages of $80,000 fall short of the $200,000 Additional Medicare Tax threshold, so that third line reads $0.00 — the surtax has not switched on yet. Adding the three pieces together, $4,960.00 plus $1,160.00 plus $0.00, gives a Total FICA tax withheld of $6,120.00 — the employee's share alone; the employer owes a matching $6,120.00 in Social Security and Medicare tax on the same $80,000, a cost that never appears on the employee's own pay stub.
Questions
Why does Social Security tax stop but Medicare tax doesn't?
Social Security tax is capped at the annual wage base ($168,600 in this calculator) because the program pays benefits tied to a bounded share of pre-retirement earnings — taxing beyond that ceiling wouldn't buy proportionally more benefit. Medicare tax has applied to every dollar of wages since Congress removed its own wage ceiling in 1994; the hospital insurance program it funds was never designed around a capped benefit, so nothing caps the tax that pays for it.
What is the Additional Medicare Tax, and who actually pays it?
It is an extra 0.9% Medicare tax on wages above $200,000, added by the Affordable Care Act in 2013 and withheld automatically once an employer's payroll crosses that figure for one employee, regardless of a spouse's income or filing status. Unlike the regular 6.2% and 1.45% pieces, the employer never matches this 0.9% — it comes out of the employee's pay alone, and true household liability is settled on the tax return against the actual filing-status threshold.
Why did my Social Security withholding stop, then start again at a new job?
Each employer applies the $168,600 wage base independently, tracking only the wages it paid. Someone who earns $100,000 at one job, changes employers mid-year, and earns another $100,000 at the second job gets the full 6.2% withheld twice — $200,000 in combined wages against a $168,600 cap means an excess $1,946.80 was over-withheld, claimed back as a credit on the federal tax return rather than refunded automatically by either employer.
How is FICA different from federal income tax withholding?
FICA is a flat-rate payroll tax — 6.2% and 1.45% regardless of income, aside from the Social Security cap and the Additional Medicare Tax — while federal income tax withholding is progressive, tied to a W-4 election and brackets that rise with income. FICA also funds two specific trust funds by law; income tax withholding is a general prepayment toward whatever the filed return eventually owes, and it can be adjusted or refunded far more freely than FICA ever is.
Does this calculator work for a self-employed person?
Not directly. Self-employed workers pay SECA tax instead of FICA — the same 12.4% Social Security and 2.9% Medicare rates, but doubled because there is no separate employer to match them, applied to net self-employment earnings rather than wages. This instrument computes only the employee-side FICA withheld from a paycheck; halve the SECA rates for a rough employee-equivalent share, but use a dedicated self-employment tax formula for an accurate figure.
Why doesn't the $200,000 Additional Medicare Tax threshold ever change?
Congress fixed it in the statute rather than indexing it to wage growth, unlike the Social Security wage base, which the Social Security Administration adjusts most years to track the national average wage index. Because the threshold stays still while typical pay rises, a slowly growing share of the workforce crosses it over time — a structural difference between the two limits inside the same tax, not an oversight.
References
- IRS — Topic no. 751, Social Security and Medicare Withholding Rates
- Social Security Administration — Contribution and Benefit Base
- IRS — Questions and Answers for the Additional Medicare Tax
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.