What determines the amount of tax withheld from your paycheck

The amount of tax your employer takes from each paycheck depends on four things: your filing status (single, married, head of household), the number of dependents you claim, your gross pay (what you earn before deductions), and the W-4 form you filled out when you were hired. Federal income tax, Social Security tax, and Medicare tax are calculated separately using different rules, so your total withholding is the sum of all three.

Your employer does not decide how much to take—they follow IRS tables that match your W-4 answers to a withholding amount. If you change your life situation (marriage, a second job, a child born), your withholding can change too, but only if you submit a new W-4. Many people never update their W-4 after hiring, which is why some get large refunds and others owe money at tax time.

Key Takeaways

  • Federal income tax withholding is based on your W-4 form, filing status, dependents, and pay amount—not a flat percentage.
  • Social Security tax is 6.2 percent of your gross pay, and Medicare tax is 1.45 percent, and both are withheld the same way every paycheck.
  • If you work a second job or your spouse works, you may be withheld too much because the IRS tables assume one income per household.
  • Updating your W-4 when your life changes (marriage, children, second job) can prevent overpaying or underpaying taxes throughout the year.
  • Your pay stub shows exactly what was withheld and why, so you can track whether the amount matches what you expect.

How federal income tax withholding is calculated

Federal income tax withholding uses a two-step process. First, your employer looks at your W-4 to find your filing status and the number of dependents you claimed. Second, they use IRS withholding tables that match your pay frequency (weekly, biweekly, monthly) to find the dollar amount to withhold. The tables are updated each year and account for the standard deduction and tax brackets.

The withholding tables assume you have only one job and that your spouse (if married) does not work. If either of those is false, the tables will withhold the wrong amount. For example, if you and your spouse both work full-time, the IRS tables will withhold as if each of you is a single earner, which means you will both be under-withheld. You can fix this by updating your W-4 to claim fewer dependents or by using the IRS Multiple Jobs Worksheet.

Your W-4 also lets you request extra withholding or claim a certain number of "allowances" (on older W-4 forms). If you want more tax taken out each paycheck—perhaps because you have side income or investment income—you can ask your employer to withhold an additional flat amount. This is useful if you know the standard withholding will not cover your total tax bill.

Social Security and Medicare taxes are fixed percentages

Unlike federal income tax, Social Security tax and Medicare tax are withheld at the same rate from every paycheck. Social Security tax is 6.2 percent of your gross pay, up to a wage cap that changes each year. Medicare tax is 1.45 percent of all your gross pay with no cap. Together, these are called FICA taxes (Federal Insurance Contributions Act).

Your employer also pays an equal amount of Social Security and Medicare tax on your behalf—that 6.2 percent and 1.45 percent come out of your check, and your employer sends the same amounts to the IRS separately. This is why your total FICA withholding appears as two line items on your pay stub: one for you, one labeled as the employer's share (which you do not see taken from your check, but it is part of your total compensation cost).

If you earn over a certain threshold (which varies by year), you may also owe an additional 0.9 percent Medicare tax on the excess. This is withheld automatically once you cross that income level in a calendar year. Self-employed people pay both the employee and employer share, which is why their total FICA rate is roughly double.

State and local taxes vary by where you live and work

In addition to federal tax, most states withhold income tax from your paycheck. The amount depends on your state's tax rate, your filing status, and dependents—similar to federal withholding but using your state's own tables. Nine states have no income tax at all (Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington, Wyoming, and New Hampshire), so residents of those states see no state income tax line on their pay stub.

Some cities and counties also withhold local income tax. New York City, Philadelphia, and Columbus, Ohio are examples of places with local tax withholding. If you work in one city but live in another, you may owe tax to both, or your employer may withhold for the city where you work. Check your pay stub to see what local taxes, if any, are being withheld.

If you move to a new state or city mid-year, contact your employer's payroll department to update your withholding. Failing to do so can result in under-withholding for your new location or over-withholding for your old one.

How to read the tax withholding on your pay stub

Your pay stub breaks down every deduction and withholding. The "gross pay" line shows what you earned before anything is taken out. Below that, you will see separate lines for federal income tax, Social Security, Medicare, state income tax, and any local taxes. Each line shows the amount withheld that pay period and often a year-to-date total.

Compare the federal income tax amount to what you expect based on your W-4. If you claimed zero dependents, the withholding should be higher than if you claimed one or more. If the amount seems wrong, check that your employer has your current W-4 on file. You can also use the IRS Withholding Calculator (available on irs.gov) to estimate what your withholding should be and compare it to what is actually being taken.

The Social Security and Medicare lines should be consistent every paycheck (unless your pay changes). If your gross pay is the same each week, your FICA withholding should be the same too. If one paycheck shows a different FICA amount, it usually means your gross pay was different that week—perhaps because of overtime, a bonus, or unpaid time off.

When to update your W-4 to change your withholding

You should file a new W-4 whenever your life situation changes in a way that affects your taxes. Common reasons include: getting married or divorced, having a child, taking a second job, your spouse starting or stopping work, buying a home, or a significant change in income. You can submit a new W-4 to your employer's payroll department at any time—it takes effect on the next paycheck.

If you received a large refund last year, you were over-withheld, meaning you gave the government an interest-free loan. Updating your W-4 to claim more dependents or request less withholding will put more money in your paycheck now instead of waiting for a refund later. Conversely, if you owed money at tax time, you were under-withheld, and you should update your W-4 to claim fewer dependents or request extra withholding.

The IRS W-4 form changed in 2020 and no longer uses "allowances." The current form asks directly about dependents, other income, and whether you want extra withholding. If you have an old W-4 on file from before 2020, your employer may ask you to update it, but you are not required to unless your withholding situation has changed.

Common reasons your withholding might be wrong

The most common reason for incorrect withholding is having more than one job. If you work two part-time jobs, each employer withholds as if that is your only income, so your combined withholding is too low. The IRS Multiple Jobs Worksheet helps you figure out how to adjust your W-4 to account for this. You can claim fewer dependents on one of the jobs, or request extra flat-dollar withholding on one of them.

Another common issue is a spouse who works. If you are married filing jointly and both spouses work, the withholding tables assume each of you is a single earner, which under-withholds for your household. Again, the Multiple Jobs Worksheet or the IRS Withholding Calculator can help you adjust. Some couples solve this by having one spouse claim all the dependents and request extra withholding, while the other claims zero.

Self-employment income, investment income, and rental income are not subject to withholding, so if you have any of these, your W-4 withholding from your job may not cover your total tax bill. You can request extra withholding on your W-4 to account for this, or you may need to make quarterly estimated tax payments to the IRS.

Frequently Asked Questions

Why is my withholding different every paycheck?

If your gross pay changes (overtime, bonus, unpaid time off), your federal income tax withholding may change too because it is calculated as a percentage of that pay. Social Security and Medicare withholding will also change if your gross pay changes. If your gross pay is the same every week but withholding varies, contact payroll to make sure your W-4 is correct.

Can I claim zero dependents to get more money withheld?

Yes. Claiming zero dependents increases your federal income tax withholding each paycheck. You can also request a specific extra dollar amount on your W-4 if you want even more withheld. This is useful if you have side income or know you will owe taxes at the end of the year.

What happens if I do not fill out a W-4?

If you do not submit a W-4, your employer must withhold as if you are single with no dependents, which is the highest withholding rate. You should fill out a W-4 as soon as possible to adjust your withholding to match your actual situation.

Does my employer keep the withheld taxes?

No. Your employer sends all withheld federal, state, and local taxes to the IRS and your state and local tax agencies on your behalf. The withheld amount is credited toward your tax bill for the year. At tax time, you reconcile what was withheld against what you actually owe.

Can I change my W-4 mid-year?

Yes. You can submit a new W-4 to your employer at any time, and it takes effect on the next paycheck. There is no limit to how many times you can update it. This is useful if your situation changes (new job, marriage, child) or if you realize your current withholding is too high or too low.