What Gets Withheld From Your Paycheck and Why

Your employer withholds payroll taxes from each paycheck based on information you provide on Form W-4 and your gross pay. The amount withheld covers federal income tax, Social Security tax (6.2% of wages), and Medicare tax (1.45% of wages). Your employer sends this money to the IRS on your behalf throughout the year so you do not owe a large bill at tax time.

The federal income tax withholding is the variable piece — it depends on your W-4 answers, your pay frequency, and your total income. Social Security and Medicare withholding are fixed percentages that apply to almost all wages. Some states and cities also withhold income tax, which follows similar logic but uses state or local forms instead.

Understanding how these amounts are calculated helps you know whether your W-4 is set correctly. If too much is withheld, you get a refund but lose access to that money during the year. If too little is withheld, you may owe money when you file your tax return.

Key Takeaways

  • Social Security tax is always 6.2% of your gross wages, and Medicare tax is always 1.45%, with no upper income limit for Medicare.
  • Federal income tax withholding depends on your W-4 answers, pay frequency, and the IRS withholding tables, and changes when you update your W-4.
  • Your gross pay is the starting number for all withholding calculations — deductions like health insurance or 401(k) contributions reduce your taxable wages for income tax but not for Social Security and Medicare.
  • You can use the IRS Withholding Calculator on irs.gov to check whether your current withholding is on track, or ask your payroll department to show you the calculation.
  • State and local income tax withholding follows the same principle as federal but uses different forms and rates that vary by where you live and work.

The Fixed Taxes: Social Security and Medicare

Social Security and Medicare withholding are the simplest to calculate because they are flat percentages with no variation. Social Security tax is 6.2% of your gross wages up to a wage base limit (in 2024, that limit is $168,600 — once you earn that much in a year, no more Social Security tax is withheld). Medicare tax is 1.45% of all your gross wages with no upper limit. Together, these are called FICA taxes.

The calculation is straightforward: take your gross pay for the pay period, multiply by 0.062 for Social Security, and multiply by 0.0145 for Medicare. If you earn $2,000 in a pay period, Social Security withholding is $124 and Medicare withholding is $29. Your employer withholds these amounts and sends them to the IRS, separate from income tax withholding.

High earners pay an additional 0.9% Medicare tax on wages above $200,000 (single) or $250,000 (married filing jointly). This additional tax is also withheld by your employer and appears on your pay stub as "Additional Medicare Tax" or similar.

How Federal Income Tax Withholding Is Calculated

Federal income tax withholding uses your W-4 form, your pay frequency, and IRS withholding tables. The process has four steps: calculate your adjusted gross pay, apply the standard deduction for your pay period, look up the withholding amount in the IRS table, and multiply by the number of pay periods in a year to annualize.

Start with your gross pay for the pay period. Subtract any pre-tax deductions — contributions to a traditional 401(k), health insurance premiums, or dependent care accounts reduce the amount subject to federal income tax withholding. This adjusted amount is your taxable wages for the pay period. (Note: Social Security and Medicare still apply to your full gross pay, not the reduced amount.)

Next, subtract the standard deduction amount for your pay frequency. The IRS publishes different standard deduction amounts for weekly, biweekly, semimonthly, and monthly pay periods. For 2024, the standard deduction for a biweekly paycheck is about $308 (this changes yearly). This step accounts for the fact that you get a standard deduction once per year, spread across all your paychecks.

Once you have the amount after the standard deduction, your employer uses the IRS withholding tables that match your filing status (single, married, head of household) and pay frequency. The table shows a range of wages and the corresponding withholding amount. Your employer finds the row that matches your taxable wages and reads across to find the withholding. This is the federal income tax withheld from that single paycheck.

What Your W-4 Changes and Why It Matters

Your W-4 form tells your employer how much federal income tax to withhold. The form has several sections: your filing status, adjustments for multiple jobs or spouse income, and an optional section where you can claim dependents or request extra withholding. Each of these changes the calculation.

If you claim yourself as a dependent on your W-4 (which most people do), you get a standard deduction amount subtracted before the withholding table is applied. If you claim additional dependents, the standard deduction increases, which lowers your withholding. If you have a spouse who also works, you may need to adjust your W-4 to avoid under-withholding. If you have two jobs, you can use the "multiple jobs" worksheet on the W-4 to calculate a safe withholding amount.

You can also request extra withholding on line 4(c) of the W-4 if you know you will owe money at tax time. This is useful if you have income your employer does not know about, such as self-employment income or investment income. The extra amount you request is withheld from every paycheck.

When you start a new job, you fill out a W-4. You can update your W-4 at any time — if your life changes (marriage, divorce, new dependent, second job), you should update it so your withholding stays accurate. Changes take effect on the next paycheck after your employer processes the new form.

State and Local Income Tax Withholding

Most states that have an income tax withhold it from your paycheck using a similar method to federal withholding. You fill out a state W-4 form (sometimes called a state tax withholding form or certificate of nonresidence) when you start a job. The state provides withholding tables and instructions to your employer, who calculates and withholds state income tax each pay period.

State withholding rates and standard deductions vary widely. Some states have a flat tax rate (Indiana, Illinois, Pennsylvania), while others use progressive brackets like the federal system (California, New York). Some states allow you to claim dependents on your state W-4, others do not. A few states have no income tax at all (Texas, Florida, Nevada, South Dakota, Tennessee, Washington, Wyoming).

If you work in a state different from where you live, you may owe tax to both states, or you may be able to claim a credit for taxes paid to the other state. This is complex and depends on the specific states involved. Your employer withholds based on where you work, not where you live, unless you file a nonresident certificate.

Some cities also withhold local income tax — New York City, Philadelphia, and Columbus are examples. Local withholding is calculated separately and appears as a line item on your pay stub. You may need to fill out a local tax form when you start work in one of these cities.

Using Your Pay Stub to Check the Calculation

Your pay stub shows the gross pay, each withholding amount, and your net pay (take-home). You can use this to verify the calculation is correct. Look for these line items: gross pay, federal income tax withholding, Social Security withholding, Medicare withholding, and any state or local tax withholding.

To check Social Security and Medicare: multiply your gross pay by 0.062 and 0.0145. The amounts on your stub should match (within a few cents due to rounding). If they are significantly different, ask your payroll department why.

To check federal income tax withholding, the math is more complex because it depends on your W-4 and the IRS tables. If you suspect the amount is wrong, use the IRS Withholding Calculator at irs.gov/taxes/individuals/tax-withholding-estimator. This tool asks about your income, filing status, dependents, and other factors, then tells you whether your current withholding is on track or whether you should adjust your W-4.

If you notice an error on your pay stub — a withholding amount that seems too high or too low, or a missing deduction — contact your payroll department immediately. Errors are usually corrected on the next paycheck, and your year-end tax forms (W-2) will reflect the correct totals.

What Happens If Withholding Is Wrong

If your employer withholds too much federal income tax during the year, you will receive a refund when you file your tax return. The IRS does not pay interest on refunds, so you lose the use of that money for months. If you consistently get large refunds, you should update your W-4 to reduce withholding and take home more pay each week.

If your employer withholds too little, you will owe money when you file your return. You may also owe a penalty if you under-withheld by a large amount. To avoid this, update your W-4 if your situation changes — a new job, a spouse starting work, a significant raise, or substantial income from other sources. You can also request extra withholding on your W-4 if you know you will have a tax bill.

Self-employed people and those with investment income often face under-withholding because their employers do not know about this income. If this applies to you, use the IRS Withholding Calculator to estimate your total tax liability, then request extra withholding on your W-4 to cover the gap.

Frequently Asked Questions

Why does my Social Security withholding stop partway through the year?

Social Security tax only applies to wages up to an annual limit (in 2024, $168,600). Once you earn that much in a calendar year, your employer stops withholding Social Security tax for the rest of the year. Medicare tax continues for all wages with no limit. If you work for multiple employers, each one withholds Social Security tax independently, which can result in over-withholding — you claim the excess on your tax return.

Can I request zero withholding on my W-4?

You can request reduced withholding, but the IRS has rules about claiming zero dependents if you are a dependent on someone else's return or if you have income above a certain threshold. If you claim zero withholding and do not meet the requirements, your employer may be required to withhold a minimum amount. Consult the W-4 instructions or a tax professional if you are unsure.

Does my 401(k) contribution reduce my Social Security and Medicare taxes?

No. A traditional 401(k) contribution reduces your federal income tax withholding because it lowers your taxable income, but Social Security and Medicare taxes still apply to your full gross pay before the 401(k) is deducted. This is why your net pay is lower than you might expect — you pay FICA taxes on the full amount, then the 401(k) is deducted from what remains.

What if I have two jobs — do I need to update my W-4 at both?

You should fill out a W-4 at each job, but you only need to claim dependents at one of them. The W-4 has a "multiple jobs" worksheet that helps you calculate safe withholding across both jobs. If you do not use the worksheet, you risk under-withholding because each employer calculates withholding as if you only have that one job. The worksheet prevents this by reducing your withholding at one or both jobs.

How often should I update my W-4?

Update your W-4 whenever your life changes: marriage, divorce, new dependent, significant raise, second job, or substantial other income. You should also review your withholding annually using the IRS Withholding Calculator to make sure you are on track. If you consistently get large refunds or owe money at tax time, that is a sign your W-4 needs adjustment.