Income tax is calculated by taking your total income, subtracting deductions you're allowed to claim, and then applying the tax rate that matches your income level

The federal government taxes income in brackets, meaning different portions of your income are taxed at different rates. If you earn $50,000, you don't pay the same rate on all $50,000 — you pay lower rates on the first portion and higher rates on income above certain thresholds. Before those rates apply, you subtract either the standard deduction (a flat amount everyone can claim) or itemized deductions (specific expenses you list out). The number you're left with is your taxable income, and that's what the tax brackets apply to.

The actual calculation happens on your tax return, which you file once a year. Most people file between January and April 15. Your employer has already withheld tax from your paychecks throughout the year based on a W-4 form you filled out, so the return either confirms that amount was correct, results in a refund if too much was withheld, or shows you owe more if too little was taken out.

Key Takeaways

  • Your taxable income is your total income minus either the standard deduction or itemized deductions — not your full gross pay.
  • Tax brackets mean you pay different rates on different portions of your income, not one flat rate on everything you earn.
  • Your employer withholds tax from each paycheck based on your W-4 form, and your annual return reconciles what was actually owed.
  • The standard deduction for 2024 is $14,600 for single filers and $29,200 for married couples filing jointly, though these amounts change each year.
  • State and local income tax is calculated separately from federal tax and varies by where you live and work.

The standard deduction and itemized deductions

Before tax brackets apply, you subtract one of two things from your income. The standard deduction is a set dollar amount that the IRS adjusts each year. For 2024, it's $14,600 for single filers, $29,200 for married couples filing jointly, and $21,900 for heads of household. You don't have to prove anything to claim it — you just subtract it from your income.

The other option is itemized deductions, which means you list out specific expenses the tax code allows you to deduct: mortgage interest, property taxes, charitable donations, and medical expenses above a certain threshold, among others. You only itemize if your total deductions add up to more than the standard deduction. Most people use the standard deduction because it's simpler and because their expenses don't exceed it.

Once you subtract one or the other from your total income, you have your taxable income. That's the number the tax brackets apply to.

How tax brackets work

The federal tax code divides income into brackets, each with its own rate. For 2024, the rates are 10%, 12%, 22%, 24%, 32%, 35%, and 37%. The brackets themselves change each year and depend on your filing status (single, married filing jointly, head of household, and so on).

The key point: you don't pay one rate on all your income. If you're single and your taxable income is $50,000, you pay 10% on the first $11,600, then 12% on the next portion up to $47,150, then 22% on the remaining amount. You're in the 22% bracket, but you don't pay 22% on all $50,000. This is why people sometimes say "I'm in the 22% bracket" — they mean that's the rate on their last dollar of income, not their overall rate.

The IRS publishes the exact bracket thresholds each year. Your tax software or a tax professional can apply them, but the math itself is straightforward once you know your taxable income and filing status.

Tax withholding from your paycheck

Your employer doesn't wait until April to collect tax. Instead, they withhold an amount from each paycheck based on the W-4 form you completed when you were hired. The W-4 asks about your filing status, how many dependents you have, and whether you have other income or deductions. Your employer uses that information to estimate how much tax you'll owe for the year and divides it by the number of pay periods.

The withholding is an estimate. If your circumstances change — you get married, have a child, take a second job, or have significant investment income — your withholding may no longer be accurate. You can update your W-4 at any time during the year, and many people do this to adjust their refund or to avoid owing money at tax time.

When you file your tax return, you report how much was withheld. If it matches what you actually owe, you break even. If too much was withheld, you get a refund. If too little was withheld, you owe the difference.

Self-employment tax and additional taxes

If you're self-employed or have income that isn't subject to withholding — like freelance work, rental income, or investment gains — you're responsible for calculating and paying tax on that income yourself. You report it on your tax return and may need to make estimated tax payments four times a year to avoid penalties.

Self-employed people also pay self-employment tax, which covers Social Security and Medicare. Employees have this withheld automatically, but self-employed people calculate it themselves. The rate is 15.3% on 92.35% of your net self-employment income, though you can deduct half of it from your income tax calculation.

Other situations can trigger additional taxes: capital gains (profit from selling investments), net investment income if you earn above a certain threshold, and alternative minimum tax if you have very high income and large deductions.

State and local income tax

Federal income tax is only part of the picture. Most states also tax income, and some cities do as well. State tax is calculated separately using your state's own brackets, standard deductions, and rules. Some states have no income tax at all (including Florida, Texas, and Wyoming), while others have rates ranging from about 1% to over 13%.

You report state income tax on a separate return filed with your state tax authority, usually at the same time you file federal taxes. Your employer withholds state tax based on a state W-4 form, similar to the federal version. If you work in one state but live in another, you may need to file returns in both places, though most states have agreements to prevent double taxation.

What happens when you file your return

On your tax return, you report your total income from all sources: wages (shown on a W-2 form from your employer), self-employment income, interest, dividends, rental income, and anything else. You then subtract either the standard deduction or your itemized deductions. The result is your taxable income.

You look up the tax on that amount using the tax tables or tax software. You then subtract any tax credits you're may have access to to — these are different from deductions because they reduce your tax dollar-for-dollar rather than reducing your income. Common credits include the Earned Income Tax Credit, child tax credit, and education credits.

Finally, you compare the tax you owe to the amount that was withheld from your paychecks. If withheld amount is more, you get a refund. If it's less, you owe the difference. You send the return to the IRS (and your state tax authority if you owe state tax) by April 15, or you can request an extension.

Frequently Asked Questions

Why do I get a refund if taxes were already withheld?

Your employer's withholding is an estimate based on the W-4 you filled out. If your actual tax liability is lower than what was withheld — because you had less income than expected, claimed deductions, or had major life changes — you get the overpayment back as a refund. It's not assistance programs; it's your own money that was withheld.

What's the difference between a tax deduction and a tax credit?

A deduction reduces your taxable income, so it saves you tax at your marginal rate. A credit reduces your tax bill directly, dollar-for-dollar. A $1,000 deduction might save you $220 in tax if you're in the 22% bracket. A $1,000 credit saves you exactly $1,000. Credits are generally more valuable.

Do I have to file a return if I didn't earn much?

You must file if your income exceeds the standard deduction for your filing status. For 2024, that's $14,600 for single filers. If you earned less and had no tax withheld, you may not be required to file, but you should if tax was withheld because you'd be due a refund.

How do investment gains get taxed differently?

Long-term capital gains (profit from selling an investment you held over a year) are taxed at lower rates than ordinary income: 0%, 15%, or 20% depending on your total income. Short-term gains (held under a year) are taxed as ordinary income at your regular bracket rate. Dividends are also taxed at preferential rates if they're may have access to dividends.

Can I change my withholding if I'm getting too big a refund?

Yes. You can update your W-4 with your employer at any time. If you're getting large refunds, you can claim more allowances or adjust the extra withholding amount to bring home more pay each period. The goal is to have your withholding match your actual tax liability as closely as possible.