In addition to federal income tax collected by the United States, most individual U.S. states collect a state income tax. Some local governments also impose an income tax, often based on state income tax calculations. Forty-two states and many localities in the United States impose an income tax on individuals. Eight states impose no state income tax, and a ninth, New Hampshire, imposes an individual income tax on dividends and interest income but not other forms of income. Forty-seven states and many localities impose a tax on the income of corporations.

The United States federal government and most state governments impose an income tax. They 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, 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. Most business expenses are deductible. Individuals may deduct certain personal expenses, including home mortgage interest, state taxes, contributions to charity, and some other items. Some deductions are subject to limits, and an Alternative Minimum Tax (AMT) applies at the federal and some state levels.