How taxes work in the United States comes down to this: federal, state, and local governments each collect their own taxes, most people’s largest bill is the federal income tax, and that tax is calculated by starting with everything you earned, subtracting specific deductions to reach taxable income, and running the result through seven progressive brackets. You pay as you go through the year via paycheck withholding or quarterly estimated payments, then reconcile on Form 1040 by April 15 of the following year.
What You Actually Pay Taxes On
The federal government collects the largest share of total tax revenue, mainly through income and payroll taxes. State and local governments lean more on sales and property taxes. The categories overlap in some places and not in others, so it helps to see them side by side before digging into the calculation.
Federal income tax applies to wages, investment income, business profits, and most other earnings. It uses a progressive rate structure, meaning each additional dollar of income can be taxed at a higher rate than the last. For 2026, rates run from 10% on the first slice of taxable income up to 37% on income above $640,600 for single filers.
State income tax varies dramatically. Some states use a flat rate, others have their own progressive brackets, and a handful impose no individual income tax at all. State rates generally range from around 3% to over 13% at the top. If you live in a state with an income tax, the same earnings are taxed by both governments.
Payroll taxes fund Social Security and Medicare. Collected under the Federal Insurance Contributions Act, they are split evenly between employer and employee: 6.2% each for Social Security (12.4% total) and 1.45% each for Medicare (2.9% total), a combined 15.3%.1Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates The Social Security portion only applies up to an annual wage base — $184,500 for 2026.2Social Security Administration. Contribution and Benefit Base Medicare has no cap, and high earners owe an extra 0.9% on wages above $200,000 single or $250,000 joint.3Internal Revenue Service. Topic No. 560, Additional Medicare Tax Self-employed people pay the full 15.3% themselves, but can deduct the employer-equivalent half when figuring adjusted gross income.4Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes)
Sales and excise taxes are imposed by state and local governments — there is no national sales tax. State rates run from zero in states like Oregon and Montana up to 7.25%, and local jurisdictions often add their own percentage, so the combined rate at the register can exceed 10% in some areas. Excise taxes are levied by both federal and state governments on specific products like gasoline, tobacco, alcohol, and airline tickets, typically built into the price you see.
Property taxes are the largest revenue source for local governments, funding schools, fire departments, and local infrastructure. The tax is based on the assessed value of real estate and is recalculated periodically. Effective rates vary enormously depending on where you live, from under 0.3% of a home’s value in some states to well over 2% in others.
Investment profits sit inside the income tax but with their own rate schedule. If you hold an asset a year or less, gains are short-term and taxed at ordinary income rates. Held longer than a year, gains are long-term and qualify for preferential rates of 0%, 15%, or 20% depending on taxable income. High earners also pay a 3.8% Net Investment Income Tax on investment income above $200,000 single or $250,000 joint, so top earners effectively pay 23.8% on long-term gains.5Internal Revenue Service. Net Investment Income Tax
How Your Federal Income Tax Is Calculated
Your federal income tax is figured in steps, each one narrowing what actually gets taxed. The calculation plays out on Form 1040, the standard individual return.6Internal Revenue Service. About Form 1040, U.S. Individual Income Tax Return
Step 1: Gross Income
Gross income is everything you earned or received during the year: wages, salaries, tips, interest, dividends, business profits, capital gains, rental income, and retirement distributions. Some income is excluded by law — interest from municipal bonds, for example, generally does not count. Gross income is the broadest measure, and it is where the IRS starts.
Step 2: Adjusted Gross Income
Adjusted gross income (AGI) is gross income minus a set of specific “above-the-line” deductions you can take whether or not you itemize later. These include Health Savings Account contributions, the deductible portion of self-employment tax, educator expenses, and student loan interest, among others. AGI matters beyond just the tax calculation. It determines your eligibility for many credits, deductions, and phase-outs throughout the return.
Step 3: Taxable Income
From AGI, you subtract either the standard deduction or your itemized deductions, whichever is larger. The result is your taxable income, the number that actually runs through the tax brackets.
For 2026, the standard deduction amounts are:7Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
- Single: $16,100
- Married Filing Jointly: $32,200
- Married Filing Separately: $16,100
- Head of Household: $24,150
Itemized deductions include home mortgage interest, charitable contributions, and state and local taxes (the SALT deduction). For 2026, the SALT deduction is capped at $40,400 for most filers, though the cap phases down for modified adjusted gross income above roughly $505,000. Itemizing only makes sense if your eligible expenses add up to more than the standard deduction.
Step 4: Apply the Brackets
Taxable income flows through seven marginal brackets. “Marginal” means only the income within each bracket is taxed at that bracket’s rate, not your entire income. Someone in the 24% bracket does not pay 24% on every dollar; their first dollars are taxed at 10%, the next slice at 12%, and so on up.
The 2026 brackets for single filers and married couples filing jointly are:7Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
- 10%: Up to $12,400 (single) / $24,800 (joint)
- 12%: $12,401–$50,400 (single) / $24,801–$100,800 (joint)
- 22%: $50,401–$105,700 (single) / $100,801–$211,400 (joint)
- 24%: $105,701–$201,775 (single) / $211,401–$403,550 (joint)
- 32%: $201,776–$256,225 (single) / $403,551–$512,450 (joint)
- 35%: $256,226–$640,600 (single) / $512,451–$768,700 (joint)
- 37%: Over $640,600 (single) / Over $768,700 (joint)
Head of Household brackets are wider than Single brackets, producing a lower tax bill and one of the main benefits of qualifying for that status. Filing status is set by your situation as of December 31 of the tax year.8Internal Revenue Service. Filing Status
Credits vs. Deductions
Deductions and credits both cut what you owe, but they work at different points in the calculation, and the dollar difference between them is enormous.
A deduction reduces the income subject to tax. Its dollar value depends on your bracket. A $1,000 deduction saves $220 for someone in the 22% bracket and $370 for someone in the 37% bracket. A credit reduces your actual tax bill dollar for dollar. A $1,000 credit saves you $1,000 regardless of bracket.
Credits come in two forms. Nonrefundable credits can reduce your tax liability to zero but no further. Refundable credits can push your liability below zero, generating a refund check. The Earned Income Tax Credit and the refundable portion of the Child Tax Credit are the most common examples that put money back in taxpayers’ pockets.
Investment losses have their own mechanism. Capital losses offset capital gains, and if losses exceed gains, you can deduct up to $3,000 of the excess against ordinary income each year and carry forward the rest.
How You Pay Through the Year
The US runs on a pay-as-you-go system. You do not wait until April to hand over a full year of tax. You pay throughout the year, and the April return reconciles what you owe against what you already sent in.
For employees, your employer withholds federal income tax and payroll taxes from each paycheck and sends them to the IRS on your behalf. The amount withheld depends on what you tell your employer on Form W-4.
If you are self-employed, earn freelance income, or have significant investment income that is not subject to withholding, you make quarterly estimated tax payments. The four due dates for each tax year are:9Internal Revenue Service. Estimated Tax
- April 15: covers income earned January through March
- June 15: covers April and May
- September 15: covers June through August
- January 15 of the following year: covers September through December
Underpaying estimated taxes triggers a penalty that functions like interest on the shortfall. It applies even if you end up owed a refund when you file.
Filing Deadline and Extensions
The standard deadline for filing your federal return is April 15 of the following year. For the 2026 tax year, that is April 15, 2027.10Internal Revenue Service. When to File If April 15 falls on a weekend or holiday, the deadline shifts to the next business day.
If you need more time, you can request an automatic six-month extension, pushing the filing deadline to October 15. Here is the part people get wrong constantly: an extension to file is not an extension to pay. You still owe any estimated tax by April 15, and penalties and interest run on anything unpaid after that date.11Internal Revenue Service. Topic No. 304, Extensions of Time to File Your Tax Return
What Happens If You File Late, Pay Late, or Cannot Pay
Two penalties can hit you if you miss the deadline, and the sizes are very different.
The failure-to-file penalty is 5% of the unpaid tax for each month or partial month the return is late, up to a maximum of 25%.12Internal Revenue Service. Failure to File Penalty The failure-to-pay penalty is much smaller: 0.5% of the unpaid balance per month, also capped at 25%.13Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges When both apply in the same month, the failure-to-file penalty is reduced by the failure-to-pay amount, so you are not hit with both at full force at once. The takeaway: even if you cannot pay, file on time. The penalty for not filing is ten times steeper per month than the penalty for not paying.
If your return understates your tax because of negligence or a substantial understatement of income, the accuracy-related penalty adds 20% of the underpayment caused by the error.14Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments For fraud, the penalty jumps to 75% of the underpayment attributable to the fraudulent conduct.15Office of the Law Revision Counsel. 26 USC 6663 – Imposition of Fraud Penalty
If you owe and cannot pay in full, ignoring the bill is the worst move. A payment plan stops the escalation. Short-term plans give you up to 180 days to pay in full with no setup fee. Longer installment agreements spread payments over months or years; the IRS charges a setup fee and continues accruing interest and a reduced failure-to-pay penalty (0.25% per month instead of 0.5%) while the plan is active. While a plan is in place, the IRS generally cannot levy your bank accounts or garnish your wages.16Internal Revenue Service. Payment Plans; Installment Agreements
How Audits Actually Happen
The federal tax system is built on voluntary compliance. You calculate your own tax, report it, and pay it, and the IRS has tools to verify what you reported.
An audit is the IRS checking your return against information it already has, like W-2s and 1099s from employers and financial institutions. Discrepancies between what you reported and what third parties reported are the most common trigger. The vast majority of audits are handled by mail: you receive a letter asking for documentation on a specific deduction or income figure, and you respond with records. In-person audits at an IRS office or your home are far less common and typically reserved for more complex returns.
How Long the IRS Can Come Back at You
The IRS does not have unlimited time. Under the standard rule, the IRS has three years from the date you filed to assess additional tax. If you omitted more than 25% of your gross income, the window extends to six years. There is no time limit at all if the return was fraudulent or if you never filed.17Internal Revenue Service. Overview of Statute of Limitations on the Assessment of Tax
The same logic works in reverse for refund claims. You generally have three years from the date you filed, or two years from the date you paid the tax, whichever is later, to claim a refund you missed.18Internal Revenue Service. Time You Can Claim a Credit or Refund After that window closes, the money is gone.
What Records to Keep and for How Long
Good records are your real protection in an audit, and the statute of limitations tells you how long to keep them. At a minimum, hold onto tax returns and supporting documents (W-2s, 1099s, receipts for deductions, investment purchase records) for at least three years from the date you filed. If you reported income from property or investments, keep the purchase records until three years after you sell and report the disposition, because the IRS needs to verify your cost basis, not just the sale price. If there is any chance the six-year rule could apply, keep records for seven years to be safe.