If you look at a paycheck and wonder where the money went before income tax even entered the picture, the answer is usually FICA. FICA stands for the Federal Insurance Contributions Act, and it is the payroll tax that funds Social Security and Medicare. It is separate from federal income tax, it comes out of nearly every paycheck, and it works on rules that surprise people the first time they understand them.
This guide breaks FICA into its two pieces, explains who pays what, and covers the wage cap and the high-earner surtax that trip up a lot of taxpayers.
FICA is two taxes, not one
FICA is really a bundle of two separate payroll taxes:
- Social Security tax, often labeled OASDI on a paystub, which stands for Old-Age, Survivors, and Disability Insurance.
- Medicare tax, which funds hospital insurance for people 65 and older and some younger people with disabilities.
Each piece has its own rate and its own rules. They are collected together, but they behave differently once income climbs, which is the part most people miss.
Who pays, and the employer match
For an employee, FICA is split between you and your employer. You pay half through payroll withholding, and your employer pays a matching half directly. You never see the employer half on your paystub, but it is a real cost of employing you, which matters when you negotiate pay or compare an employee role to contract work.
The combined employee-plus-employer Social Security rate and the combined Medicare rate are set by statute. As an employee you are responsible for your share, withheld automatically each pay period. A paycheck calculator shows the FICA lines alongside federal and state withholding so you can see exactly how gross pay becomes net pay.
The arrangement changes completely if you are self-employed, which we cover below.
The Social Security piece and its wage cap
The defining feature of the Social Security tax is the wage base limit, sometimes called the wage cap. Social Security tax applies only to earnings up to an annual ceiling. Once your wages for the year cross that ceiling, no more Social Security tax comes out, and your take-home pay jumps for the rest of the year.
The ceiling is indexed and rises most years, so we deliberately avoid quoting a single figure here, but the mechanic is what matters:
- Below the cap, every dollar of wages is subject to Social Security tax.
- Above the cap, none is.
- The cap resets each January, so the tax restarts at the top of every year.
This is why a high earner sometimes notices a larger paycheck in the back half of the year. They have hit the cap and stopped paying the Social Security portion. The Medicare portion keeps going.
A second wrinkle: the cap is per employer if you change jobs or hold two jobs. Each employer withholds Social Security up to the cap on the wages it pays, so someone with two jobs can over-pay across the year. The excess is recovered as a credit when you file your annual return.
The Medicare piece has no cap
Medicare tax works differently. There is no wage ceiling. Medicare tax applies to every dollar of earned income, no matter how high. A surgeon earning ten times the Social Security cap still pays Medicare tax on the entire amount.
On top of the base Medicare tax, high earners owe an Additional Medicare Tax. Once wages cross a threshold that depends on filing status, an extra slice of Medicare tax applies to the wages above that line. Two features make this surtax easy to get wrong:
- Employers do not match it. The Additional Medicare Tax is an employee-only charge.
- Employer withholding is mechanical, not personalized. Your employer is required to start withholding the surtax once the wages it pays you cross the threshold, but it does not know your filing status or your spouse’s income. A dual-income married couple can end up under-withheld or over-withheld, and the true amount is reconciled on the annual return.
If your household has two high incomes or you switched jobs mid-year, the surtax is a common reason your withholding does not match your final bill.
Self-employment: you pay both halves
When you work for yourself, there is no employer to pay the matching half of FICA, so you pay it yourself. This combined amount is called self-employment tax, and it covers both the employee and employer shares of Social Security and Medicare.
That sounds harsh, and the headline rate is roughly double the employee FICA rate, but two adjustments soften it:
- You compute self-employment tax on a slightly reduced share of your net business profit rather than on gross revenue.
- You can deduct the employer-equivalent half of the self-employment tax from your income when figuring federal income tax. This deduction does not reduce the self-employment tax itself, but it lowers your income tax.
The wage cap and the Medicare surtax still apply to self-employment income, layered together with any W-2 wages you also earn. A self-employment tax calculator handles the reduced base and the deductible half so you can estimate what to set aside, and a federal income tax calculator shows how the deduction flows through to your income tax.
A worked example
Imagine an employee earning $60,000 in wages for the year, well under the Social Security cap. Using illustrative rates of 6.2 percent for the employee Social Security share and 1.45 percent for Medicare:
| Tax | Base | Rate | Amount |
|---|---|---|---|
| Social Security (employee) | $60,000 | 6.2% | $3,720 |
| Medicare (employee) | $60,000 | 1.45% | $870 |
| Total FICA withheld | $4,590 |
The employer separately pays another $4,590 to match. None of this is federal income tax, which is calculated on a different base after deductions. FICA comes off the top of earned income with no standard deduction to shield it, which is why even low earners who owe little or no income tax still see FICA taken from every check.
What FICA does not touch
FICA is a tax on earned income, wages and self-employment profit. It generally does not apply to:
- Investment income such as interest, dividends, and capital gains.
- Retirement distributions from a 401(k) or IRA.
- Most rental income.
This is one reason the source of your income matters so much for total tax. A dollar of wages carries FICA on top of income tax, while a dollar of long-term capital gains carries neither FICA nor ordinary income tax rates. High earners with significant investment income face a separate Net Investment Income Tax instead, but that is a distinct levy, not part of FICA.
Frequently asked questions
Is FICA the same as federal income tax?
No. FICA funds Social Security and Medicare and is calculated on earned income from the first dollar, with no standard deduction. Federal income tax is calculated separately on taxable income after deductions, using progressive brackets. Both can appear on the same paystub as different lines.
Why did my paycheck get bigger late in the year?
You probably hit the Social Security wage cap. Once your year-to-date wages cross the ceiling, the Social Security portion of FICA stops, so your take-home pay rises until the cap resets in January. The Medicare portion keeps coming out.
Do I get FICA back like an income tax refund?
Generally no. FICA is not refundable the way over-withheld income tax is. The one exception is over-payment of Social Security tax when you hold two or more jobs and your combined wages exceed the cap. That excess is credited on your annual return.
Does everyone pay FICA?
Most employees and self-employed people do, but there are narrow exceptions, including certain state and local government workers covered by their own pension systems, some student employees, and specific visa categories. The default assumption for ordinary W-2 wages and self-employment profit is that FICA applies.
The bottom line
FICA is two taxes wearing one name. The Social Security piece stops at a wage cap that resets each year. The Medicare piece never stops and adds a surtax for high earners that employers do not personalize. If you are self-employed you pay both halves as self-employment tax, with a partial deduction to ease the income-tax side. Understanding which income is earned, and therefore subject to FICA, explains a large share of the gap between your gross pay and what actually lands in your account.