Income taxes in the United States are imposed by the federal government, and most states. The income taxes are determined by applying a tax rate, which may increase as income increases, to taxable income, which is the total income less allowable deductions. Income is broadly defined. Individuals and corporations are directly taxable, and estates and trusts may be taxable on undistributed income. Partnerships are not taxed (with some exceptions in the case of Federal income taxation), but their partners are taxed on their shares of partnership income. Residents and citizens are taxed on worldwide income, while nonresidents are taxed only on income within the jurisdiction. Several types of credits reduce tax, and some types of credits may exceed tax before credits. An alternative tax applies at the federal and some state levels.

In the United States, the term "payroll tax" usually refers to FICA taxes that are paid to fund Social Security and Medicare, while "income tax" refers to taxes that are paid into state and federal general funds.

Most business expenses are deductible. Individuals may also deduct a personal allowance (exemption) and certain personal expenses, including home mortgage interest, state taxes, contributions to charity, and some other items. Some deductions are subject to limits.

Capital gains are taxable, and capital losses reduce taxable income to the extent of gains (plus, in certain cases, $3,000 or $1,500 of ordinary income). Individuals currently pay a lower rate of tax on capital gains and certain corporate dividends.

Taxpayers generally must self assess income tax by filing tax returns. Advance payments of tax are required in the form of withholding tax or estimated tax payments. Taxes are determined separately by each jurisdiction imposing tax. Due dates and other administrative procedures vary by jurisdiction. April 15 following the tax year is the last day for individuals to file tax returns for federal and many state and local returns. Tax as determined by the taxpayer may be adjusted by the taxing jurisdiction.