US Income Tax Explained for Beginners: Brackets, Deductions, Credits and the W-4

The US federal income tax can look complicated, but the core idea is simple: you add up your income, subtract deductions, and apply progressive rates to what is left, in layers. This guide explains each step with a worked example, using the federal figures for tax year 2025 (the return you file in 2026). The IRS adjusts the numbers every year, so always check the current tables before you file.

Step 1: Gross income

Gross income includes wages, self-employment income, interest, dividends, rent, capital gains and most other income, from any source. Employers report wages on Form W-2, and banks and brokers report other income on 1099 forms.

Step 2: Filing status

Your status sets your standard deduction and your brackets: single, married filing jointly, married filing separately, head of household, or qualifying surviving spouse. Choose the one that applies to your situation on the last day of the year.

Step 3: Deductions

You subtract either the standard deduction or your itemised deductions, whichever is larger. For tax year 2025, the standard deduction is $15,750 for single filers and $31,500 for married couples filing jointly, with additional amounts for age 65 or older and for blindness. Itemising makes sense when mortgage interest, state and local taxes (within a cap), charitable gifts and large medical costs add up to more than the standard deduction.

Step 4: Apply the brackets

Each rate applies only to the slice of income inside its bracket, not to your whole income. For a single filer in tax year 2025, taxable income is taxed as follows.

Earning more never lowers your take-home pay: moving into a higher bracket only taxes the extra dollars at the higher rate.

A worked example

A single employee earns $75,000 in wages and takes the standard deduction.

That is an effective rate of about 10.6% of wages, even though the top slice of income is taxed at 22%. This is the difference between the marginal rate (22%) and the effective rate. You can run your own numbers in the tax bracket calculator.

Payroll taxes: FICA

Separately from income tax, employees pay Social Security tax at 6.2% on wages up to an annual wage base and Medicare tax at 1.45% on all wages, 7.65% in total. Employers pay a matching amount. Self-employed people pay both halves, which is 15.3% on net earnings, with a deduction for half of it.

Credits reduce tax directly

A credit cuts your tax bill dollar for dollar, so it is worth more than a deduction of the same size. Common ones are the Child Tax Credit, the Earned Income Tax Credit, education credits and the credit for child and dependent care. Some are refundable, meaning you get the money even if you owe no tax, and many phase out at higher incomes.

The W-4 and withholding

When you start a job you fill in Form W-4, which tells your employer how much federal tax to withhold from each paycheque. If too little is withheld, you owe money at filing and possibly a penalty. If too much, you get a refund, which is an interest-free loan to the government. The IRS offers an online estimator to help you set the form. Update it after a marriage, a new child, a second job or a large change in income.

Deadlines and filing

• The deadline for individual returns is usually April 15, or the next business day. An extension to October gives more time to file but not to pay.
• File electronically for the fastest refund. Free filing options exist for people under an income limit.
• Keep records of income, receipts and forms for at least three years.

State taxes and other forms

Most states have their own income tax with different rules, and a few have none. Sales tax is separate: estimate it with our sales tax calculator. If you are a nonresident alien or on a visa, different forms and rules can apply, such as Form 1040-NR and the substantial presence test, so check your status.

This is general information, not tax advice. For your specific situation, consult a tax professional or the IRS website.

Frequently asked questions

How do US tax brackets work?

Each rate applies only to the part of your income inside that bracket, so higher income is taxed at higher rates only on the additional amount.

What is the standard deduction for 2025?

$15,750 for single filers and $31,500 for married couples filing jointly, for tax year 2025.

What is the difference between a deduction and a credit?

A deduction reduces taxable income, while a credit reduces the tax itself dollar for dollar.

What is FICA?

Payroll taxes for Social Security and Medicare, totalling 7.65% for employees.

When is the tax filing deadline?

Usually April 15, with an extension available to file by October.

What is a W-4 for?

It tells your employer how much federal tax to withhold from your pay.

Last reviewed 8 November 2026. Rates, limits and rules change, so confirm figures with the official source before you act.