On a U.S. paycheck, FICA and FIT are two separate federal deductions that work in completely different ways. FICA (the Federal Insurance Contributions Act tax) is a flat 7.65% of your wages that funds Social Security and Medicare. FIT (federal income tax withholding) is a variable amount your employer pulls from each check to pre-pay your annual income tax, calculated from what you reported on your W-4. The short version of FICA vs FIT: one is a fixed percentage that everyone pays at the same rate, and the other is an estimate tailored to your personal tax situation.
How Each One Shows Up on Your Pay Stub
Payroll systems label these deductions inconsistently. Your Social Security portion of FICA may appear as OASDI, FICA, SS, or SOCSEC. The Medicare portion often shows as MED or FICA-MED. Federal income tax withholding commonly appears as FIT, FED, FITW, or FWT. The standard breakdown is three federal line items: one for Social Security, one for Medicare, and one for income tax.
What FICA Covers and How It’s Calculated
FICA is a flat-rate payroll tax split into two pieces: 6.2% for Social Security and 1.45% for Medicare, for a combined employee rate of 7.65%.1Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates Those rates don’t shift based on your filing status, dependents, or anything else on your W-4. Every employee pays the same percentage on the same dollar of wages.
Your employer matches your FICA contribution dollar for dollar, adding another 7.65% on top of what you pay.2Social Security Administration. Social Security and Medicare Tax Rates The full 15.3% is what actually funds the programs; you only see your half on the stub.
The Social Security Wage Cap
Social Security tax applies only up to an annual wage cap. For 2026, you pay the 6.2% Social Security tax on the first $184,500 you earn.3Social Security Administration. Contribution and Benefit Base Once your year-to-date wages cross that threshold, your employer stops withholding Social Security tax for the rest of the year, and your paychecks get slightly larger. Medicare has no cap. The 1.45% applies to every dollar you earn.
The Extra Medicare Tax for High Earners
An additional 0.9% Medicare tax kicks in once your wages exceed $200,000 in a calendar year ($250,000 if married filing jointly, $125,000 if married filing separately).4Internal Revenue Service. Topic No. 560, Additional Medicare Tax Above that line, your effective Medicare rate on the excess wages climbs from 1.45% to 2.35%. Your employer does not match this surcharge; it comes entirely from your paycheck.
One quirk worth noting: your employer is required to start withholding the extra 0.9% once your individual wages pass $200,000, regardless of your filing status. If you’re married filing jointly and your own wages don’t reach the $250,000 joint threshold, you can claim the excess withholding back as a credit when you file.5Internal Revenue Service. Questions and Answers for the Additional Medicare Tax
What FIT Is and How It’s Calculated
FIT is the estimated portion of your annual federal income tax that your employer sends to the IRS on your behalf each pay period.6Internal Revenue Service. Tax Withholding for Individuals Unlike FICA’s fixed percentage, FIT depends on how much you earn, your filing status, and the credits and deductions you claim. Two people with identical salaries can have very different FIT amounts on their stubs.
Federal income tax uses a progressive structure, so your income is taxed in layers at rising rates rather than one flat percentage. Your employer’s payroll system estimates the total tax you’ll owe for the year and spreads the withholding across your paychecks.
Your W-4 Is the Control
Your employer calculates FIT from what you report on IRS Form W-4, the Employee’s Withholding Certificate.7Internal Revenue Service. Form W-4, Employee’s Withholding Certificate The form captures your filing status, whether you work multiple jobs, the number of dependents you claim, and any extra amount you’d like withheld. Choosing “Married Filing Jointly” generally results in less FIT withheld per paycheck than “Single” at the same salary, because the joint brackets are wider.
If you have qualifying children under 17, Step 3 of the W-4 lets you factor in the Child Tax Credit, worth $2,200 per child for 2026, which directly reduces the FIT pulled from each check. You can also request a flat extra dollar amount be withheld every pay period if you want a cushion at tax time. Skip filing a W-4 entirely and your employer must withhold as though you’re a single filer with no credits, which is the highest default level.8Internal Revenue Service. Topic No. 753, Form W-4, Employees Withholding Certificate
The IRS offers a free Tax Withholding Estimator that walks through your income, deductions, and credits, then generates a pre-filled W-4 to hand to your employer.9Internal Revenue Service. Tax Withholding Estimator It’s the most reliable way to get withholding right after a life change like marriage, a new child, or a second job.
Reconciliation Happens at Filing Time
Because FIT is only an estimate, the final accounting happens when you file Form 1040. Withhold more than your actual liability and you get a refund. Withhold too little and you owe the difference, and possibly a penalty. A big refund isn’t really a win; it means you gave the government an interest-free loan all year. Landing close to zero, with a small refund or small balance due, is the goal.
Why Pre-Tax Deductions Shrink FICA and FIT Differently
Some paycheck deductions reduce your taxable wages before FICA and FIT are calculated, but the rules aren’t the same for both. This is where confusion usually starts, because your W-2 can show different wage figures in different boxes.
Health insurance premiums paid through a Section 125 cafeteria plan (which covers most employer-sponsored coverage) reduce wages for both FICA and FIT. Every dollar going to premiums shrinks your Social Security, Medicare, and income tax withholding.10Internal Revenue Service. FAQs for Government Entities Regarding Cafeteria Plans
Traditional 401(k) contributions work differently. Your pre-tax 401(k) deferrals reduce wages for FIT, lowering income tax withholding, but they do not reduce wages for FICA. You still owe Social Security and Medicare tax on those contributions.11Internal Revenue Service. Retirement Plan FAQs Regarding Contributions That’s why Box 1 on your W-2 (wages for income tax) is often lower than Boxes 3 and 5 (wages for Social Security and Medicare). If those numbers don’t match, pre-tax retirement contributions are almost always the reason.
Dependent care assistance (up to $7,500 for 2026) and qualified commuter transit and parking benefits (up to $340 per month each for 2026) reduce both FICA and FIT wages when offered through a qualifying plan. Group-term life insurance coverage over $50,000 works in the opposite direction: the excess gets added back to your wages for both taxes.12Internal Revenue Service. Employer’s Tax Guide to Fringe Benefits
If You’re Self-Employed, Neither Gets Withheld
The FICA vs FIT split assumes you’re a W-2 employee. If you’re self-employed, no one withholds anything from your income and you handle both pieces yourself. The self-employment equivalent of FICA is SECA tax. Because there’s no employer to split the cost, you pay both halves: 12.4% for Social Security and 2.9% for Medicare, totaling 15.3% on your net self-employment earnings, with the same $184,500 Social Security wage cap and the same 0.9% additional Medicare tax at higher income levels.13Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes) Income tax gets paid through quarterly estimated payments due April 15, June 15, September 15, and January 15 rather than through paycheck withholding.14Internal Revenue Service. 2026 Form 1040-ES – Estimated Tax for Individuals
Fixing a W-2 That Looks Wrong
By early the following year, your employer must give you a Form W-2 summarizing total gross wages and the exact amounts withheld for FIT, Social Security, and Medicare.15Internal Revenue Service. Topic No. 752, Filing Forms W-2 and W-3 That’s the official record you’ll use to file your return. If something looks wrong — a bad Social Security number, incorrect wages, or a withholding amount that doesn’t match your pay stubs — ask your employer for a corrected Form W-2c before you file.16Social Security Administration. Helpful Hints to Forms W-2c/W-3c Filing Filing a return with numbers you already know are wrong just creates a second problem to untangle.