Social Security and Medicare are federal taxes, but they are not part of federal income tax. Your paycheck is hit by two separate federal systems: federal income tax, which funds general government operations, and FICA taxes, which fund Social Security and Medicare specifically. Both are federal. Both are mandatory for most workers. But they use different rates, different rules, and different boxes on your W-2.
How Federal Income Tax and FICA Differ
Federal income tax is progressive. The rate climbs as your income rises, and the money goes into the government’s general fund. Your employer estimates what you owe based on your Form W-4 and withholds it from each paycheck, and you settle the final number when you file your return.
FICA works differently. The letters stand for the Federal Insurance Contributions Act, and the tax funds two specific programs: Social Security and Medicare. The rates are flat, not progressive. Every dollar collected goes into the trust funds behind those programs rather than the general fund.
Your W-2 keeps them separate so you can see exactly where your money went. Box 2 shows federal income tax withheld. Box 4 shows Social Security tax. Box 6 shows Medicare tax.1Internal Revenue Service. General Instructions for Forms W-2 and W-3 (2026) – Section: Specific Instructions for Form W-2
One more distinction matters for how you think about the two systems. FICA applies only to earned income: wages, salaries, bonuses, tips. Investment income like dividends, interest, and capital gains is not subject to Social Security or Medicare tax. Federal income tax, by contrast, applies to both earned and unearned income.
Social Security Tax
The Social Security portion of FICA is officially the Old-Age, Survivors, and Disability Insurance (OASDI) tax. The total rate is 12.4% of covered wages, split evenly: 6.2% from you and 6.2% from your employer.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates
Social Security tax stops at an annual earnings cap known as the wage base limit. For 2026, that cap is $184,500.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates Once your wages for the year cross that line, neither you nor your employer owes any more Social Security tax on additional earnings. The maximum an employee can have withheld in 2026 is $11,439.1Internal Revenue Service. General Instructions for Forms W-2 and W-3 (2026) – Section: Specific Instructions for Form W-2
Medicare Tax
The Medicare portion of FICA, formally the Hospital Insurance tax, is 2.9% of covered wages, split as 1.45% employee and 1.45% employer. There is no wage base limit for Medicare, so every dollar of earned income is taxed.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates
The Additional Medicare Tax for High Earners
Higher earners owe an extra 0.9% Medicare surtax on wages above certain thresholds, bringing the employee-side rate to 2.35% on income past the cutoff. The thresholds depend on filing status:3Internal Revenue Service. Topic No. 560, Additional Medicare Tax
- Single or head of household: $200,000
- Married filing jointly: $250,000
- Married filing separately: $125,000
Your employer does not know your filing status for this purpose. The law requires the employer to begin withholding the extra 0.9% once your wages cross $200,000 in a calendar year, regardless of whether you are married or single.4eCFR. 26 CFR 31.3102-4 – Special Rules Regarding Additional Medicare Tax If you are married filing jointly and your combined wages exceed $250,000, you reconcile the difference on your return. The employer does not match the additional 0.9%; it falls entirely on the employee.
If You’re Self-Employed
Without an employer to pay half, self-employed workers pay both sides of FICA through the self-employment tax. The total is 15.3%: 12.4% Social Security and 2.9% Medicare.5Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes)
A detail people miss: the tax is not calculated on 100% of your net earnings. You first multiply net self-employment income by 92.35%, then apply the 15.3% rate.6Internal Revenue Service. Topic No. 554, Self-Employment Tax The 12.4% Social Security portion still stops at the $184,500 wage base for 2026. The 2.9% Medicare portion has no cap, and the 0.9% Additional Medicare Tax kicks in above the same filing-status thresholds that apply to wages.7Internal Revenue Service. Questions and Answers for the Additional Medicare Tax
You can deduct the employer-equivalent half of your self-employment tax when calculating adjusted gross income. This is an above-the-line deduction on Schedule 1 of Form 1040. It reduces your AGI and your federal income tax, but not the self-employment tax itself.5Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes)
Self-employment tax is not withheld from your income the way FICA is withheld from a paycheck. You pay estimated taxes quarterly on Form 1040-ES. The 2026 due dates are April 15, June 15, and September 15 of 2026, plus January 15, 2027.8Internal Revenue Service. Form 1040-ES (2026) Filing your 2026 return by February 1, 2027 with the full balance paid lets you skip the January payment.
When Social Security Benefits Themselves Are Taxed
The two federal systems eventually meet on the other side. After paying FICA throughout your career, the Social Security benefits you collect in retirement may themselves be subject to federal income tax. Whether they are depends on your provisional income, which is your adjusted gross income plus any tax-exempt interest plus half of your Social Security benefits.
Single filers with provisional income between $25,000 and $34,000 may owe federal income tax on up to 50% of their benefits. Above $34,000, up to 85% becomes taxable. For married couples filing jointly, the 50% bracket begins at $32,000 and the 85% bracket at $44,000.9Internal Revenue Service. IRS Reminds Taxpayers Their Social Security Benefits May Be Taxable These thresholds have never been adjusted for inflation, so a larger share of retirees crosses them every year.
You can ask the Social Security Administration to withhold federal income tax from your monthly benefit using Form W-4V. The permitted rates are 7%, 10%, 12%, or 22%, and no other percentage is allowed.10Internal Revenue Service. Form W-4V (Rev. January 2026) – Voluntary Withholding Request
Deductions on Your Pay Stub That Aren’t Federal
Some pay stubs list additional withholdings that look like federal taxes but are not. In roughly 18 jurisdictions, employers withhold contributions for state disability insurance or paid family leave programs at rates that generally run from about 0.2% to 1.3% of wages. These are state-level programs and do not appear alongside FICA on your W-2. If a line item on your stub does not match what you see on your W-2 as federal income tax, Social Security, or Medicare, it is almost certainly a state program rather than federal tax.