How federal income tax works

Your tax comes from a short chain of subtractions

Every return follows the same order. Start with income, subtract what the law excludes, subtract a deduction, run the rest through the brackets, then subtract credits. Compare the result with what you already paid.

Each section below takes one link in the chain. You can follow along with your own numbers in the income tax calculator.

Brackets tax layers of income, never all of it

A higher bracket applies only to the income inside it. In the example, taxable income of $49,900 fills the layers like this:

So this person is in the 12% bracket, yet pays 8.2% of their wages in income tax. The first number is the marginal rate, which applies to the next dollar. The second is the effective rate, which describes the whole year.

This answers a worry that comes up around raises. A single filer at $66,000 has $49,900 of taxable income, just under the $50,400 line where the 22% bracket starts. A $2,000 raise crosses that line, and income tax rises by only $390. With $153 of payroll tax, they keep $1,457 of the raise. No bracket can make a raise cost you money.

There's a real version of this problem, though it comes from elsewhere. Some credits and deductions shrink as income rises, which can make the next dollar more expensive than your bracket suggests. Check those limits if your income is close to one.

Your filing status sets the size of each layer

The same income can produce very different tax, because filing status changes both the standard deduction and the width of each bracket. Joint brackets are generally about twice as wide as single ones through the 24% rate, so one earner in a couple pays much less than a single person at the same pay.

You don't simply pick the one with the lowest tax, since each status has its own rules. If you aren't sure which fits, the IRS has a short filing status tool.

A deduction lowers your income, and its value depends on your bracket

A deduction saves you about your marginal rate times the amount. That means the same deduction is worth more to someone earning more. A credit, covered next, comes straight off the tax.

You take either the standard deduction or your itemized deductions, whichever is larger. For 2026, the standard deduction is $16,100 for single filers, $32,200 for joint filers, and $24,150 for heads of household.

The trap is assuming every deductible dollar saves you money. A married couple earning $150,000 who have $28,000 of mortgage interest, state and local taxes, and gifts would owe the same $15,340 as with no itemized deductions at all, since they'd take the standard deduction. Raising that to $36,000 saves $836, not $7,920, because only the $3,800 above the standard deduction counts. Keep that in mind when someone says a mortgage is good for your taxes.

Some reductions work regardless of that choice. Traditional 401(k) contributions come out before you reach this step, as the example showed. New federal deductions for tax years 2025 to 2028 are also open to people who don't itemize: up to $25,000 for qualified tips, up to $12,500 for the premium part of overtime ($25,000 joint), and up to $6,000 a person for those 65 and older. Each has its own income limit and rules, listed on the IRS page.

A credit comes straight off your tax, and some can pay you back

A $1,000 credit cuts your bill by $1,000 at any income. For 2026, the child tax credit is up to $2,200 for each qualifying child under 17, and it starts to phase out above $200,000 of income ($400,000 joint). Other dependents may qualify for a credit of up to $500.

A couple with two young children and $150,000 of wages owes $10,940, down from $15,340: a drop of $4,400.

Part of the child credit is refundable, up to $1,700 a child, so it can pay you even if you owe no tax. You need at least $2,500 of earned income to get that part. A couple with two children and $35,000 of wages has $280 of tax before credits. The credit wipes that out, and the refundable part pays another $3,400.

The earned income tax credit is another one that can raise your refund, for low- to moderate-income workers. The calculators on this site don't model it or education credits, so don't rely on them if you may qualify. The IRS's EITC Assistant checks your eligibility.

Social Security and Medicare are a separate bill

Payroll tax doesn't use brackets, deductions, or credits. You pay 6.2% for Social Security on wages up to $184,500 in 2026, and 1.45% for Medicare on all wages. Your employer pays a matching amount. A traditional 401(k) doesn't reduce it.

At lower incomes, this is often the bigger tax. A single filer earning $40,000 owes $2,620 in income tax and $3,060 in payroll tax. So a low income tax bill doesn't mean a low total tax bill.

If you're self-employed, you pay both shares, for a 15.3% rate, and no one withholds it. You generally owe it once net earnings reach $400.

Withholding is a prepayment that your W-4 controls

Your employer sends an estimate of your tax to the IRS with each paycheck, based on your Form W-4. It's only an estimate, and the return settles the real amount. The IRS suggests reviewing the form each year and whenever your situation changes. The 2026 form was also updated for the new federal deductions, so you can reflect them in your withholding.

A household with two paychecks is where this easily goes wrong. Each employer assumes it's your only job, so both apply the full standard deduction and start at the low brackets. Say two spouses earn $70,000 and $50,000, and both check "married filing jointly" without completing Step 2.

Closing that $4,220 gap would take about $162 a check in extra withholding at one job. The IRS Tax Withholding Estimator handles this and can produce a pre-filled W-4. Have your latest pay stubs ready, along with your spouse's. To see the effect on a single check, try the paycheck calculator.

A refund is your own money coming back

A refund means you prepaid more than you owed. It's not a bonus, and a bigger one doesn't mean you paid less tax. Take the single filer from the start of this guide, with $5,740 of tax. If $8,140 was withheld, the refund is $2,400. That's about $92 per biweekly check that could have been in their account during the year.

Some people like the forced savings, and that's a fair choice. If you carry card debt, though, you're paying interest while that money sits with the IRS. To bring it home instead, lower your withholding with a new W-4, and check it with the estimator so you don't overshoot.

Owing at filing isn't a failure either, as long as you don't face a penalty. You generally avoid the underpayment penalty if you owe less than $1,000, or if you paid at least 90% of this year's tax or 100% of last year's, whichever is smaller. For this filer, 90% would be $5,166. The prior-year test rises to 110% for higher earners.

On timing, the IRS says to expect a refund about 3 weeks after you e-file, or 6 weeks or more after it receives a paper return. Corrections or extra review can make it longer.

A short checkup you can do each year

1. Run your income through the income tax calculator to estimate what you'll owe.
2. Compare that with the federal income tax withheld so far on your latest pay stub, projected to year-end.
3. If the gap is large in either direction, use the IRS estimator and give your employer a new W-4.
4. Before year-end, see whether a traditional 401(k) or IRA contribution would lower your tax. The 401(k) calculator and IRA calculator show the trade-offs.
5. Check the deductions and credits you may have newly qualified for, especially after a new child, a new job, or turning 65.

Some situations call for a person. An enrolled agent or CPA can help with a business, a home sale, or an IRS notice. VITA and TCE sites offer free help to those who qualify. VITA sites generally serve people making about $70,244 or less, and TCE focuses on people 60 and older. This guide is general education, not tax advice, and your figures may differ.

Common questions

Sources

1. Revenue Procedure 2025-32: 2026 inflation-adjusted tax items · Internal Revenue Service
2. Federal income tax rates and brackets · Internal Revenue Service
3. Topic no. 501, Should I itemize? · Internal Revenue Service
4. Child Tax Credit · Internal Revenue Service
5. One Big Beautiful Bill Act: tax deductions for working Americans and seniors · Internal Revenue Service
6. Topic no. 751, Social Security and Medicare withholding rates · Internal Revenue Service
7. Self-employment tax (Social Security and Medicare taxes) · Internal Revenue Service
8. Publication 15-T (2026), Federal Income Tax Withholding Methods · Internal Revenue Service
9. Tax Withholding Estimator · Internal Revenue Service
10. Underpayment of estimated tax by individuals penalty · Internal Revenue Service
11. Refunds · Internal Revenue Service
12. Free tax return preparation for qualifying taxpayers · Internal Revenue Service