FICA vs federal income tax on a paycheck

FICA is the employee share of Social Security and Medicare. It is a set percentage of wages, with a wage cap on Social Security. Federal income tax withholding is a separate calculation that uses filing status, the standard deduction, brackets, and W-4 credits. Mixing those two lines is the most common reason people think “dependents did nothing” or “Social Security went down when I got married.” Dependents and filing status change income tax. They do not change FICA rates.

2026 employee rates used on this site

• Social Security: 6.2% of wages up to $184,500. After that wage base, the 6.2% employee share stops for the rest of the calendar year at that employer (combined wages across jobs can still hit the cap; reconciliation happens at filing if too much was withheld).
• Medicare: 1.45% of all wages. There is no Medicare wage base.
• Additional Medicare Tax: 0.9% on wages above $200,000. Employers start withholding that extra 0.9% when wages at that job pass $200,000. The employer does not match the extra 0.9%.

Your employer also pays a matching 6.2% Social Security (up to the same wage base) and 1.45% Medicare. That match is a cost of employment. It does not appear as a deduction from your take-home pay. Self-employed people pay both halves through self-employment tax; this calculator is built for wages on a Form W-2, not Schedule C net profit.

Why the Social Security line can shrink late in the year

If you earn past $184,500 in 2026 at one job, later checks stop taking the 6.2%. Take-home jumps even though the job did not give you a raise. Medicare usually continues. People sometimes read that jump as a tax-law change. It is the wage base. This site annualizes a single salary, so a $190,000 salary will show Social Security only on the first $184,500 for the year, spread across the pay periods you chose. A real payroll system stops the 6.2% on the check that crosses the cap, so the pattern across the year looks different even when the annual total is close.

Pre-tax benefits and FICA

Some benefits reduce Social Security and Medicare wages; some do not. Traditional 401(k) contributions typically reduce income tax wages but still count as FICA wages. A Section 125 health premium often reduces both income tax and FICA wages. This calculator does not model either case. If your stub’s Social Security wage is lower than gross, a pre-tax benefit is usually why. See why a stub will not match.

Why the calculator splits the lines

On the paycheck calculator, federal income tax, Social Security, and Medicare are shown separately so you can see which piece moved. Add children under 17: federal tax should fall; FICA should stay. Switch single to married jointly on the same salary: federal tax should fall because the standard deduction and brackets change; FICA should stay. If both move, something else is going on (a different gross, a different year, or a stub that already includes state tax in a combined “taxes” line).

More on the income-tax side: federal withholding and Form W-4. This is an educational estimate, not a payroll system and not IRS software.