Federal income tax is a tax on the money you earn, collected by the U.S. Internal Revenue Service (IRS) throughout the year

When you work, your employer withholds a portion of your paycheck and sends it to the federal government. If you're self-employed, you send payments directly to the IRS. At the end of the year, you file a tax return that calculates how much you actually owe based on your total income, and the government either refunds the difference or bills you for what you still owe.

Federal income tax is separate from Social Security and Medicare taxes (called payroll taxes), which also come out of your paycheck. It's also separate from state income tax, which some states charge and others don't. This guide covers only the federal tax the IRS collects.

Key Takeaways

  • Federal income tax is withheld from your paycheck by your employer and sent to the IRS throughout the year.
  • The amount you owe depends on how much you earned and your filing status, not on a flat rate everyone pays.
  • You file a tax return each year to report your income and either get money back or pay what you still owe.
  • Self-employed people and gig workers pay federal income tax directly to the IRS in quarterly installments, not through an employer.

How the federal tax system calculates what you owe

The U.S. uses a progressive tax system, which means the tax rate increases as your income increases. You don't pay one flat percentage on all your money. Instead, your income is divided into brackets, and each bracket has its own rate.

For example, in 2024, a single person might pay 10% on the first $11,000 of income, 12% on income between $11,000 and $44,725, and higher percentages on income above that. The brackets change each year and depend on your filing status (single, married filing jointly, head of household, and so on).

Before the tax is calculated, you can reduce your taxable income in two ways. The standard deduction is a fixed amount you can subtract from your income without itemizing expenses—for 2024, it's around $14,000 for a single person and $28,000 for married couples filing jointly, though these amounts change yearly. Alternatively, you can itemize deductions if you have large expenses like mortgage interest or charitable donations that add up to more than the standard deduction.

When and how much your employer withholds

Your employer uses a form called the W-4 to determine how much federal tax to withhold from each paycheck. You fill out the W-4 when you start a job, and you can update it anytime—for example, if you get married, have a child, or take a second job.

The W-4 asks about your filing status, dependents, and other income sources. Based on your answers, the IRS provides a withholding calculation that tells your employer how much to hold back. If you withhold too much, you'll get a refund when you file your return. If you withhold too little, you'll owe money.

Some people claim "exempt" on the W-4, which means no federal tax is withheld from their paycheck. This is only legal if you had no tax liability the previous year and expect to have none in the current year—typically only applies to people with very low income or certain students.

Self-employed and gig workers pay differently

If you're self-employed, run a business, or earn income from gig work (driving, freelancing, selling items online), no employer withholds tax for you. Instead, you're responsible for paying federal income tax directly to the IRS in four quarterly estimated tax payments, usually due in April, June, September, and January.

You calculate your estimated tax by projecting your annual income and subtracting deductions, then dividing by four. If you underpay, you may owe penalties and interest when you file your annual return. If you overpay, you'll get a refund.

Self-employed people also pay both the employer and employee portions of Social Security and Medicare tax (called self-employment tax), which is separate from federal income tax. You can deduct half of your self-employment tax when calculating your federal income tax.

Filing your tax return and getting a refund or paying what you owe

Every year by April 15, you file a federal tax return with the IRS. The most common form is the 1040. On it, you report all income you received during the year—from your W-2 (if you're an employee), 1099 forms (if you're self-employed or a contractor), interest, dividends, and other sources.

You then subtract your deductions (either the standard deduction or itemized deductions) to get your taxable income. You calculate the tax owed on that income using the tax tables or software, subtract the amount already withheld throughout the year, and the result is either a refund or a balance due.

You can file on your own using free software (the IRS provides a list of IRS Free File partners for people under certain income thresholds), hire a tax preparer, or use paid software. If you file late or owe money you don't pay, the IRS charges interest and penalties.

Who does not pay federal income tax

Not everyone pays federal income tax. If your income is below the standard deduction for your filing status, you generally owe no federal income tax. For 2024, a single person under age 65 with income below about $14,000 typically owes nothing. A married couple filing jointly with income below about $28,000 typically owes nothing.

Some types of income are also exempt from federal tax—for example, certain disability benefits, workers' compensation, and gifts. However, interest, dividends, and capital gains are taxable even if your wages are low.

If you're unsure whether you need to file, the IRS website has an interactive tool, or you can speak with a tax preparer. Filing even when you don't owe can be worthwhile if you're due a refund or if you claim the Earned Income Tax Credit (EITC), a refundable credit for lower-income workers.

Frequently Asked Questions

Why do I get a refund if I already paid taxes through withholding?

Your employer withholds based on an estimate, not your actual tax bill. If you withheld more than you owe—because you had less income than expected, claimed dependents, or had large deductions—the IRS refunds the overpayment. A refund means you gave the government an interest-free loan during the year.

What's the difference between federal income tax and FICA taxes?

Federal income tax goes to the general Treasury and funds government operations. FICA taxes (Social Security and Medicare) are separate payroll taxes that fund those specific programs. Both come out of your paycheck, but they're calculated and used differently.

Do I have to file a tax return if I'm self-employed?

Yes, if your net self-employment income is $400 or more in a year, you must file a federal return. Even if you're below that threshold, filing may be worth it if you're due a refund or can claim the EITC.

Can I change my W-4 withholding mid-year?

Yes. You can submit a new W-4 to your employer anytime. This is useful if your life changes—you get married, have a child, take a second job, or realize you're withholding too much or too little.

What happens if I don't file or pay federal income tax?

The IRS can assess penalties, charge interest on unpaid tax, and take collection actions like wage garnishment or seizing tax refunds. Filing late or paying late costs more than paying on time. If you can't pay in full, the IRS offers payment plans and other options.