The Basic Formula: Gross Pay Minus Tax Withholdings

Payroll tax calculation starts with your gross pay — the total amount your employer pays you before any deductions. From that amount, your employer withholds federal income tax, Social Security tax, and Medicare tax. The withholding amounts depend on three things: your gross pay for that pay period, the tax rates set by law, and the information you provided on your W-4 form when you were hired.

Your employer does not choose how much to withhold. The IRS publishes withholding tables and formulas that employers must follow. If you work in a state with income tax, your state also publishes withholding tables. Your employer runs your gross pay through these tables using your filing status and the number of dependents you claimed on your W-4, and the result is the amount withheld from your check.

The math is straightforward once you know the rates. Federal income tax withholding varies by income level and filing status. Social Security tax is a flat 6.2% of your gross pay (up to an annual earnings cap). Medicare tax is a flat 1.45% of your gross pay with no cap. State income tax rates vary by state — some states have no income tax at all.

Key Takeaways

  • Your employer withholds taxes based on your gross pay, your W-4 form, and tax tables published by the IRS and your state.
  • Social Security tax is always 6.2% of gross pay up to the annual earnings limit, and Medicare tax is always 1.45% with no limit.
  • Federal income tax withholding depends on your filing status, number of dependents, and income level — it is not a flat percentage.
  • You can change your withholding by submitting a new W-4 form to your employer if you expect to owe money or want a larger refund.
  • Self-employed people calculate payroll taxes differently because they pay both the employee and employer portions of Social Security and Medicare.

Federal Income Tax Withholding: How the IRS Tables Work

Federal income tax withholding is not a fixed percentage. Instead, the IRS publishes withholding tables organized by pay frequency (weekly, biweekly, monthly), filing status (single, married, head of household), and the number of dependents you claimed. Your employer looks up your gross pay in the table that matches your situation and reads across to find the withholding amount.

The tables are designed so that by the end of the year, the total amount withheld from your paychecks roughly matches the total federal income tax you actually owe. If you claim zero dependents, more money is withheld. If you claim more dependents, less is withheld. The W-4 form you fill out when hired tells your employer which table row to use.

The withholding tables change each year because tax brackets and standard deductions change. Your employer receives updated tables from the IRS, usually in late fall for the following year. If you change jobs, you fill out a new W-4 with your new employer — the withholding does not carry over.

Social Security and Medicare: Fixed Percentages With One Limit

Social Security and Medicare taxes are simpler than federal income tax because they are flat percentages with no variation based on filing status or dependents. Social Security tax is 6.2% of your gross pay. Medicare tax is 1.45% of your gross pay. Your employer withholds these amounts from every paycheck.

Social Security tax has an annual earnings cap. In 2024, you pay Social Security tax only on the first $168,600 of earnings in a calendar year. Once you reach that cap, no more Social Security tax is withheld from your paychecks for the rest of that year. Medicare tax has no cap — it is withheld on all earnings, no matter how high.

If you earn more than $200,000 (or $250,000 if married filing jointly), an additional 0.9% Medicare tax is withheld. This is separate from the standard 1.45% Medicare tax and applies to all earnings above the threshold. Your employer is responsible for calculating and withholding this additional amount.

State Income Tax Withholding: Rules Vary by Location

State income tax withholding works similarly to federal withholding — your employer uses state tax tables to determine the amount. However, the rules differ significantly by state. Nine states have no income tax at all: Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington, Wyoming, and New Hampshire (which taxes only dividends and interest, not wages).

In states that do tax income, the withholding tables and rates vary. Some states use a flat tax rate — for example, Colorado taxes all income at 4.4%. Others use progressive brackets similar to the federal system. Your employer must withhold based on the state where you work, not where you live, unless your state has a reciprocal agreement with your work state.

You provide state withholding information on a state W-4 form, which may be different from your federal W-4. Some states use the federal W-4 information; others require a separate form. If you work in multiple states during a year, you may need to file returns in more than one state.

What Happens When You Change Your W-4

If you find that too much or too little tax is being withheld, you can submit a new W-4 form to your employer. The new withholding takes effect on the next paycheck after your employer processes the form, usually within one to two pay periods. You do not need your employer's permission — the W-4 is your instruction to them about how much to withhold.

Common reasons to change your W-4 include getting married or divorced, having a child, taking a second job, or expecting a large refund or tax bill. The IRS provides a W-4 calculator on its website that walks you through your situation and recommends a withholding amount. You can change your W-4 as many times as you need during the year.

Changing your W-4 does not change the taxes you owe — it only changes how much is withheld from your paychecks. If you owe $3,000 in federal income tax for the year, you owe that amount regardless of your W-4. Adjusting your W-4 just determines whether that $3,000 comes out gradually through withholding or in a lump sum when you file your return.

Self-Employment Taxes: You Pay Both Sides

If you are self-employed, you calculate payroll taxes differently because you pay both the employee and employer portions of Social Security and Medicare. An employee pays 6.2% Social Security and 1.45% Medicare; the employer pays an equal amount. When you are self-employed, you pay both — 12.4% for Social Security and 2.9% for Medicare, totaling 15.3%.

Self-employed people calculate these taxes on net self-employment income, which is your business income minus business expenses. You report this on Schedule SE (Self-Employment Tax) when you file your tax return. The amount you owe is due when you file your return in April, though you may need to make quarterly estimated tax payments if you expect to owe more than $1,000.

You can deduct half of your self-employment tax as a business expense on your tax return, which reduces your taxable income. This partially offsets the fact that you are paying both the employee and employer portions. Self-employed people do not have an employer withholding taxes, so managing quarterly payments and setting aside money throughout the year is important to avoid a large bill at tax time.

Frequently Asked Questions

Why is my paycheck less than I expected?

Your paycheck is your gross pay minus all withholdings: federal income tax, Social Security, Medicare, state income tax (if applicable), and any voluntary deductions like health insurance or retirement contributions. If you claimed zero dependents on your W-4, more federal income tax is withheld. If you recently started a job or got a raise, the withholding may feel larger because you are seeing the full impact for the first time.

What if I work in two states during the same year?

You withhold taxes based on where you work, not where you live. If you work in two states, your employer in each state withholds based on that state's rules. When you file your tax return, you may owe taxes in both states or be able to claim a credit for taxes paid to one state. Some states have reciprocal agreements that simplify this — check your state's tax agency website for details.

Can I avoid withholding by claiming exempt on my W-4?

The "exempt" option on older W-4 forms allowed people to claim no federal income tax withholding if they had no tax liability the previous year and expected none in the current year. The current W-4 form does not use the word "exempt," but you can indicate you expect zero tax liability. This is only correct if you truly owe no federal income tax — using it incorrectly can result in penalties and a large bill at tax time.

Do I get back the taxes withheld from my paycheck?

Not automatically. Taxes withheld from your paycheck are held by the government until you file your tax return. If you withheld more than you owe, you receive a refund. If you withheld less than you owe, you pay the difference. The goal of withholding is to match your actual tax liability as closely as possible so you break even at tax time.