What gets taken out of your paycheck and why

Your employer calculates payroll taxes by applying federal and state tax rates to your gross pay — the total amount you earn before any deductions. The calculation happens in a specific order: federal income tax withholding first, then Social Security tax (6.2% of gross pay up to an annual cap), then Medicare tax (1.45% of all gross pay), then state and local taxes if your state or city has them. Your employer sends these amounts to the government on your behalf throughout the year, which is why you see them listed separately on your pay stub.

The actual dollar amount withheld depends on three things: how much you earn, what you claimed on your W-4 form when you started the job, and which state and city you work in. Federal income tax withholding is not a flat percentage — it uses tax brackets, so someone earning $35,000 a year pays a different rate than someone earning $75,000. Social Security and Medicare are simpler: they are the same percentage for everyone, though Social Security stops once you hit the annual wage cap (which changes each year).

Key Takeaways

  • Federal income tax withholding is calculated using tax brackets and your W-4 answers, not a single percentage rate.
  • Social Security tax is 6.2% of your gross pay up to an annual wage cap that changes yearly; Medicare tax is 1.45% of all gross pay with no cap.
  • Your W-4 form controls how much federal tax your employer withholds — claiming more allowances means less withheld, claiming fewer means more withheld.
  • State and local taxes vary by location and are calculated separately from federal taxes using their own rates and rules.
  • Your pay stub shows the gross amount, each tax withheld, and your net pay — the amount you actually receive.

How federal income tax withholding is calculated

Federal income tax withholding uses the W-4 form you fill out when hired. On that form, you claim allowances (or dependents, depending on the version) and note any extra income or jobs. Your employer uses your answers plus IRS withholding tables to calculate how much federal tax to remove from each paycheck. The tables account for your pay frequency (weekly, biweekly, monthly) and your filing status (single, married, head of household).

The withholding tables are built on tax brackets. If you are single and paid biweekly, the IRS table shows different withholding amounts for different pay ranges. Someone earning $800 biweekly is in a lower bracket than someone earning $2,000 biweekly, so the second person has more withheld. If you claim more allowances on your W-4, the employer subtracts a standard amount per allowance before applying the table, which lowers your withholding. If you claim fewer allowances, less is subtracted, and more is withheld.

You can change your W-4 at any time during employment. If you find that too much is being withheld (you get a large refund each year), you can claim more allowances. If too little is being withheld (you owe money at tax time), you can claim fewer allowances or request extra withholding on the form.

Social Security and Medicare tax calculations

Social Security tax is 6.2% of your gross pay, calculated on every dollar you earn up to an annual wage cap. In 2024, that cap is $168,600 — meaning once you have earned $168,600 in a calendar year, no more Social Security tax is withheld from your remaining paychecks that year. The cap changes annually based on wage growth. If you work for two employers in the same year, each employer withholds 6.2% up to the cap independently, which can result in overpayment; you claim the overage as a credit when you file your tax return.

Medicare tax is 1.45% of your gross pay with no annual cap — it is withheld on every dollar you earn, all year. There is also an additional Medicare tax of 0.9% that applies to wages above $200,000 (single filers) or $250,000 (married filing jointly). Your employer withholds this additional tax automatically once your year-to-date earnings cross the threshold. Unlike Social Security, there is no refund for overpayment; the additional Medicare tax is final.

Both Social Security and Medicare are calculated on your gross pay before any other deductions. Health insurance premiums, retirement contributions, and other pre-tax deductions do not reduce the amount subject to these taxes.

State and local tax calculations

State income tax withholding varies widely because not all states have an income tax. Nine states have no state income tax at all: Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington, Wyoming, and New Hampshire (which taxes only dividends and interest). The remaining 41 states each have their own tax rates, brackets, and rules. Some states use a flat percentage; others use brackets like the federal system.

Your employer withholds state tax based on your state of residence and your W-4 equivalent form (often called a state W-4 or IT-4). If you work in a state different from where you live, the rules depend on your state's reciprocal agreements with neighboring states. Some cities also impose local income tax — Philadelphia, New York City, and Columbus, Ohio are examples — and your employer withholds that separately.

State and local taxes are calculated independently from federal taxes. Your federal withholding does not reduce the amount subject to state tax, and vice versa. If you move to a different state mid-year, you should update your W-4 with your employer to adjust withholding for your new state's tax rate.

Reading your pay stub and understanding the numbers

Your pay stub lists your gross pay at the top, then shows each deduction line by line. You will see federal income tax (labeled FIT or Fed Tax), Social Security (labeled SS or FICA-SS), Medicare (labeled Med or FICA-Med), and state and local taxes if applicable. Each line shows the amount withheld from that paycheck and often a year-to-date total. At the bottom is your net pay — the amount you actually receive in your bank account or check.

The year-to-date totals are useful for tracking whether your withholding is on track. If you are paid biweekly and it is mid-year, your year-to-date federal withholding should be roughly half of what you expect to owe for the full year. If it is significantly higher or lower, you may want to adjust your W-4. The year-to-date Social Security total should stop growing once you hit the annual wage cap; after that, only Medicare and income taxes are withheld.

Some pay stubs also show deductions that are not taxes — health insurance, retirement plan contributions, flexible spending account contributions. These are subtracted from your gross pay before federal and state income tax are calculated (if they are pre-tax deductions), but Social Security and Medicare are still calculated on your full gross pay.

What happens if your withholding is wrong

If your employer withholds too much federal tax throughout the year, you receive a refund when you file your tax return. If too little is withheld, you owe money. The IRS does not charge interest or penalties if your withholding is close to your actual tax liability, but if you significantly underpay, penalties can apply. Most people adjust their W-4 to get closer to zero refund or owed amount, though some prefer to have extra withheld as a forced savings method.

Self-employed people and those with investment income or multiple jobs often need to make estimated tax payments quarterly because their employers do not withhold taxes. Employees with significant non-wage income should also consider adjusting their W-4 or making estimated payments to avoid a large bill at tax time.

If you receive a large refund year after year, you are giving the government an interest-free loan. Updating your W-4 to claim more allowances puts more money in your paycheck now. If you owe money year after year, you should claim fewer allowances or request extra withholding to avoid penalties and interest charges.

Frequently Asked Questions

Why is Social Security tax capped but Medicare is not?

Social Security is a benefit program where your payments are tied to your future benefits — higher earners receive higher benefits, but there is a maximum benefit amount. Medicare is a health insurance program with no benefit cap, so the tax continues on all income. The cap on Social Security is adjusted annually based on wage growth in the economy.

Do pre-tax deductions like health insurance reduce my Social Security and Medicare taxes?

No. Social Security and Medicare taxes are calculated on your gross pay before any deductions. Pre-tax deductions like health insurance premiums and 401(k) contributions reduce your federal and state income tax, but not Social Security or Medicare tax.

What if I work in one state but live in another?

You generally pay income tax to the state where you work, not where you live. However, some states have reciprocal agreements that allow residents to pay tax to their home state instead. Your employer should withhold based on your work location unless you provide documentation of a reciprocal agreement. Check your state's tax agency website for specifics.

Can I change my W-4 in the middle of the year?

Yes. You can submit a new W-4 to your employer at any time, and the new withholding takes effect on your next paycheck. If you realize mid-year that you are withholding too much or too little, updating your W-4 is the fastest way to adjust.

Why do I owe taxes if my employer already withheld federal tax?

Withholding is an estimate based on your W-4 answers. If your actual tax liability is higher than what was withheld — because you have investment income, a spouse with income, or you claimed too many allowances — you owe the difference. Filing your tax return calculates your true liability and reconciles it against what was withheld.