What Gets Deducted and Why

Payroll tax deductions come out of your paycheck before you see the money. Your employer withholds federal income tax, Social Security tax (6.2% of gross pay), and Medicare tax (1.45% of gross pay). Some states and cities also withhold income tax. These are not optional — they are required by law, and your employer sends them to the government on your behalf.

The amount withheld depends on three things: your gross pay (the total before any deductions), the tax rates set by law, and information you provided on your W-4 form. The W-4 tells your employer how many dependents you claim and whether you have other income or jobs. The more dependents you claim, the less federal tax is withheld. If you claim zero dependents, more is withheld.

Social Security and Medicare taxes are straightforward — they are a fixed percentage of every dollar you earn, up to an annual cap for Social Security. Federal income tax withholding is more complex because it depends on your W-4 choices and your pay frequency (weekly, biweekly, monthly, etc.).

Key Takeaways

  • Social Security tax is always 6.2% of your gross pay, and Medicare tax is always 1.45%, with no deductions or exemptions.
  • Federal income tax withholding is calculated using IRS tables that change based on your pay frequency, gross pay, and the number of dependents you claimed on your W-4.
  • State and local income taxes, if your location has them, are calculated separately using your state or city's own tax tables and rates.
  • Your employer is required to withhold these amounts and send them to the government; you cannot opt out of Social Security and Medicare taxes.
  • If too much or too little is withheld during the year, you will owe money or receive a refund when you file your tax return.

How Federal Income Tax Withholding Is Calculated

Your employer uses the IRS withholding tables to calculate federal income tax. These tables account for your pay frequency (weekly, biweekly, semimonthly, or monthly), your gross pay for that period, and your W-4 information. The IRS updates these tables each year, and employers must use the current version.

The calculation works like this: your employer takes your gross pay, subtracts the standard deduction amount for your pay period (this amount varies by frequency), and then applies the tax rate from the IRS table. If you claimed dependents on your W-4, your employer subtracts an additional amount for each dependent before calculating the tax. The result is the federal income tax withheld from that paycheck.

Example: If you are paid biweekly and earn $2,000 gross, your employer subtracts the standard deduction for biweekly pay (roughly $235 in 2024, though this changes yearly), leaving $1,765. They then apply the tax rate from the IRS table for your filing status. If you claimed one dependent, they subtract an additional dependent amount before calculating. The final number is what is withheld.

If you have a second job, work only part of the year, or have significant non-wage income, your withholding may be wrong because the tables assume you work the same job all year. In these cases, you can adjust your W-4 to increase or decrease withholding, or you can have extra tax withheld by entering an amount on line 4(c) of the W-4.

Social Security and Medicare Tax Deductions

These two taxes are the simplest to calculate because they are flat percentages with no adjustments for dependents or filing status. Social Security tax is 6.2% of your gross pay, up to a wage cap that changes each year (in 2024, the cap is $168,600). Once you earn that much in a calendar year, no more Social Security tax is withheld for the rest of the year.

Medicare tax is 1.45% of all your gross pay with no cap. If you earn over $200,000 as a single filer (or $250,000 married filing jointly), an additional 0.9% Medicare tax is withheld on the income above that threshold. This additional tax has no cap and continues for the rest of your life, regardless of income.

Both taxes are withheld from every paycheck automatically. You cannot claim exemptions or adjust the amount withheld. Your employer matches these amounts (paying an equal 6.2% for Social Security and 1.45% for Medicare), but that matching amount does not come out of your paycheck — it is a separate employer cost.

State and Local Income Tax Deductions

If you live in a state or city with income tax, your employer will also withhold for those taxes. The calculation method varies by location. Some states use a flat percentage (like Illinois at 4.95%), while others use tax brackets similar to federal tax. Cities like New York and Philadelphia also withhold local income tax.

You provide state and local withholding information on your state W-4 form, which is separate from the federal W-4. Some states do not have an income tax (Florida, Texas, Wyoming, and others), so no state withholding occurs. If you work in one state but live in another, the rules depend on where you work — your employer withholds based on the state where you earn the income.

State and local tax rates and brackets change periodically, so your employer must use the current tables. If you move during the year or change jobs, you may need to file a new state W-4 to adjust your withholding.

How to Check Your Withholding

Your pay stub shows the gross pay, each deduction (federal, Social Security, Medicare, state, local, and any others), and the net pay you receive. Add up the federal income tax, Social Security, and Medicare amounts from several recent pay stubs to see the pattern. If the amounts seem too high or too low, you can use the IRS Withholding Calculator on the IRS website to estimate whether your withholding is correct.

The calculator asks for your filing status, income, dependents, and other jobs or income. It then tells you whether you are likely to owe money or receive a refund. If the calculator shows you will owe a large amount or get a large refund, you can adjust your W-4 to change your withholding. You can file a new W-4 with your employer at any time — you do not have to wait until the new year.

Keep in mind that withholding is an estimate. Your actual tax bill depends on your full-year income, deductions, and credits, which you calculate when you file your tax return. If you withheld too much, you get a refund. If you withheld too little, you owe the difference.

Common Reasons Withholding Goes Wrong

The most common reason is a change in life circumstances that you did not report on a new W-4. If you got married, had a child, got divorced, or took a second job, your withholding may no longer be correct. The W-4 you filled out years ago does not automatically update.

Another reason is working multiple jobs. The IRS withholding tables assume you work one job all year. If you have two jobs, each employer withholds based only on that job's pay, and the total withholding may be too low because neither employer knows about the other income. You can fix this by having extra tax withheld on one or both W-4s.

Self-employment income, investment income, and other non-wage income are also not accounted for in payroll withholding. If you have significant income from these sources, you may owe tax when you file your return. You can adjust your W-4 to have extra federal tax withheld to cover this.

Frequently Asked Questions

Why is my Social Security tax the same every paycheck but my federal income tax changes?

Social Security is a flat 6.2% with no adjustments, so it is the same unless your gross pay changes. Federal income tax is calculated using IRS tables that account for your cumulative pay over the year, so the amount can vary slightly from paycheck to paycheck, especially near the end of the year or if your pay is irregular.

Can I stop Social Security and Medicare taxes from being withheld?

No. These taxes are mandatory for all employees and self-employed people. You cannot claim exemptions or opt out. Your employer must withhold them by law.

What does "net pay" mean on my pay stub?

Net pay is your take-home amount — your gross pay minus all deductions (federal, state, local, Social Security, Medicare, and any others like health insurance or retirement contributions). This is the amount deposited into your bank account or mailed as a check.

If I claim zero dependents on my W-4, will I definitely not owe taxes?

Claiming zero dependents increases withholding, but it does not may provide you will not owe. If you have significant non-wage income, multiple jobs, or other tax situations, you could still owe. Filing your tax return is the only way to know for certain.

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

Yes. You can file a new W-4 with your employer at any time. The new withholding takes effect on the next paycheck. There is no penalty for changing your W-4 multiple times during the year.