What are FICA and OASDI? The paycheck taxes decoded

FICA — the Federal Insurance Contributions Act — is the payroll tax that funds Social Security and Medicare. On your pay stub it usually appears as two lines: OASDI (Old-Age, Survivors, and Disability Insurance — that's Social Security) and Medicare. Together they take 7.65% of your wages, your employer quietly pays a matching 7.65%, and none of it is affected by your W-4, deductions, or filing status. It is the flattest, least avoidable tax most Americans pay — and the one most likely to prompt the question 'what is this line item?'

What you're buying with it

Unlike income tax, FICA is tied to specific programs — and to your own future benefits. OASDI funds Social Security retirement checks, disability insurance, and survivor benefits for spouses and children. Paying it earns you 'credits' (in 2026, one credit per roughly $1,900 of covered wages, up to four a year), and 40 credits — about ten working years — is what qualifies you for retirement benefits later. Your benefit amount is computed from your 35 highest earning years, which is why FICA is better thought of as forced insurance premiums than as pure tax. The Medicare portion funds hospital insurance (Part A) that most people receive premium-free at 65.

The cap: why high earners see a mid-year raise

The 6.2% OASDI tax applies only to wages up to an annual limit — $184,500 in 2026, adjusted upward most years. Earn beyond that and the Social Security line simply stops for the rest of the year, producing the famous phantom raise in late-year paychecks for high earners. Medicare has no cap, and above $200,000 of wages your employer must withhold an extra 0.9% Medicare surtax (the true threshold is $250,000 for married couples filing jointly, so two-earner couples sometimes owe more at filing, and some single filers get a small refund of it).

Self-employed? You pay both halves

Employees split FICA with their employer; the self-employed are both parties, paying 15.3% as self-employment tax (12.4% OASDI up to the cap + 2.9% Medicare). Two softeners: the tax applies to 92.35% of net self-employment earnings, not the full amount, and half of the tax is deductible against income tax. It's still routinely the largest tax surprise for new freelancers — a gig worker netting $60,000 owes roughly $8,500 of self-employment tax before income tax even enters the picture.

• FICA is charged on gross wages before most deductions — your 401(k) contribution reduces income tax but not FICA. The notable exceptions: Section 125 'cafeteria plan' items like health insurance premiums, FSA contributions, and payroll HSA contributions do escape FICA, which is a quiet extra ~7.65% return on funding an HSA through payroll rather than directly.
• Multiple jobs can overwithhold OASDI: each employer applies the cap independently, so two jobs totaling over $184,500 can withhold too much Social Security — the excess comes back as a credit on your tax return.
• Some public employees don't pay OASDI at all because their state pension system opted out decades ago; they build no Social Security credits for those years.
• Students working at their own school, and a few other narrow categories, are FICA-exempt — one reason campus-job paychecks look surprisingly whole.

The bottom line

FICA is 7.65% of every paycheck — 6.2% Social Security on wages up to $184,500 (2026) plus 1.45% Medicare on everything, with an employer match behind the scenes and both halves landing on the self-employed. It buys disability coverage now, survivor protection for your family, and a retirement benefit built from your 35 best years. You can't opt out and you can't deduct your way around it; the only real moves are using payroll-based HSA and cafeteria-plan benefits, recovering overwithholding from multiple jobs, and keeping your earnings record accurate so the insurance you've been buying all along pays what it should.