What Is FICA?

Almost everyone who has looked closely at a pay stub has noticed that the numbers do not add up the way they expect. You know your salary, you have some sense of your tax bracket, and yet the deductions are larger than the bracket alone would suggest. The gap is usually FICA — a tax that works on completely different principles from income tax and is frequently mistaken for part of it.

This guide explains what FICA is, why it is calculated on gross wages, and the two features that produce most of the confusion: the wage base and the Additional Medicare Tax. The paycheck calculator shows income tax and FICA side by side on your own figures.

The problem this guide solves

Two federal taxes come out of every paycheck and they behave nothing alike.

Federal income tax is progressive. It applies to taxable income — gross pay minus the standard deduction — and rises in bands as income increases. Your bracket describes the rate on the last dollar, as covered in tax brackets explained.

FICA is flat. It applies to gross wages with no deduction subtracted first, at a fixed rate that does not change with income — except at the wage base, where part of it stops entirely, and above a high threshold, where a small additional amount begins.

Because FICA ignores the standard deduction, it starts from the first dollar you earn. A part-time worker with no income tax liability at all still pays FICA on every hour worked. This is why take-home pay is lower than a bracket calculation predicts, and why for many low and middle earners payroll tax is the larger of the two federal deductions.

What FICA funds

FICA has two components serving different programs.

Social Security — formally Old-Age, Survivors, and Disability Insurance — funds retirement benefits, survivor benefits for dependants of deceased workers, and disability benefits. Your contributions build a record of covered earnings that determines your eventual benefit.

Medicare funds hospital insurance for people aged 65 and over and for certain younger people with disabilities.

Both are financed on a pay-as-you-go basis: today's payroll taxes largely fund today's beneficiaries rather than sitting in an account with your name on it. Your contribution record determines your entitlement, not a balance you own.

The rates and how they apply

The employee side has three pieces.

Social Security is charged at a fixed rate on wages up to an annual ceiling, known as the contribution and benefit base or simply the wage base. Earnings above that ceiling attract no further Social Security tax. The base is adjusted each year in line with national average wages; the current figure this site uses is listed on the data sources page.

Medicare is charged at a lower fixed rate on all wages, with no ceiling. Every dollar you earn is subject to it, however high your income.

Additional Medicare Tax adds a further 0.9% on wages above a threshold that varies by filing status. Two details make it unusual: employers withhold it once wages pass a set amount regardless of your actual filing status, and there is no employer match on this portion. The thresholds are fixed by statute and, unlike most tax figures, are not adjusted for inflation — so more people cross them each year in real terms.

Employers match the Social Security and Medicare contributions, so the total reaching the programs is roughly double what your stub shows. Economists generally argue the employer share is ultimately borne by workers through lower wages, but it does not appear on your payslip.

A worked example

Take someone earning $100,000 a year, paid biweekly, with no pre-tax deductions.

FICA at the combined employee rate of 7.65% on gross wages comes to $7,650 for the year — $6,200 for Social Security and $1,450 for Medicare. Across 26 pay periods that is roughly $294 per paycheck.

Note what did not happen. The standard deduction was not subtracted. No bracket was applied. The calculation is simply the rate multiplied by gross pay, which is why it is so much simpler than income tax and so much harder to reduce.

Now suppose the same person contributes $10,000 to a traditional 401(k). Their income tax falls, because taxable income drops. Their FICA does not change at all, because the contribution is still wages for payroll tax purposes. The 401(k) calculator models the retirement side of that trade, and how a 401(k) works covers the plan itself.

What happens at the wage base

This is the feature that generates the most confused questions to payroll departments.

Once your year-to-date wages pass the Social Security wage base, that portion of FICA stops for the rest of the calendar year. Take-home pay rises, sometimes noticeably, with no change to your salary or your withholding elections.

Then, on 1 January, it starts again from zero. A high earner can therefore see net pay jump in, say, October and fall back in January — a pattern that looks like an error and is not.

Medicare continues throughout, with the Additional Medicare Tax layering on top once wages pass its own threshold. The two ceilings are unrelated and sit at very different levels.

Common mistakes

Assuming your tax bracket describes total withholding. It describes income tax only. FICA sits on top and is calculated on a different base.

Expecting pre-tax retirement contributions to cut FICA. They reduce income tax, not payroll tax. Certain health and dependent care benefits do reduce FICA wages; 401(k) contributions do not.

Thinking FICA is refundable. It is not withholding against a year-end calculation. The main exception is Social Security over-withheld across multiple employers, reconciled when you file.

Treating self-employment tax as unrelated. It funds the same two programs, with the self-employed paying both halves because no employer matches.

Assuming the Additional Medicare threshold is inflation-adjusted. It is fixed by statute, so its real value falls every year.

Believing your contributions sit in a personal account. They fund current beneficiaries and build an earnings record that determines your entitlement.

Practical tips

Read your pay stub line by line once. Separating income tax withholding from Social Security and Medicare makes every subsequent payroll question easier to answer.

If your net pay changes mid-year without an obvious cause, check whether you have crossed the wage base or the Additional Medicare threshold before contacting payroll.

If you hold more than one job and your combined wages exceed the wage base, expect to reclaim over-withheld Social Security when you file — neither employer can see the other's payroll.

Review your Social Security earnings record periodically. Benefits are calculated from reported earnings, and errors are far easier to correct close to when they happen.

If you have significant freelance income alongside a job, plan for self-employment tax explicitly rather than meeting it as a surprise at filing time.

Where to go next

See income tax and FICA together on your own salary with the paycheck calculator. Convert an annual figure into take-home across pay frequencies with the salary calculator, or start from an hourly rate with the hourly to salary calculator.

For the income tax side alone, use the federal income tax calculator and read marginal vs effective tax rate. For the full picture of what is deducted before you are paid, see gross vs net pay. More tools sit in the salary hub.

This guide is educational and does not constitute financial or tax advice. Consult a qualified professional about your own situation.