Income tax in the United States

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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 (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. 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.

The federal government has imposed an income tax since the ratification of the Sixteenth Amendment to the United States Constitution was ratified in 1913, and 42 US states impose state income taxes. Income taxes are levied on wages as well as on capital gains, and fund federal and state governments. Payroll taxes are levied only on wages, not gross incomes, but contribute to reducing the after-tax income of most Americans. The most common payroll taxes are FICA taxes that fund Social Security and Medicare. Capital gains are currently taxable at a lower rate than wages, and capital losses reduce taxable income to the extent of gains.

Taxpayers generally must determine for themselves the income tax that they owe by filing tax returns. Advance payments of tax are required in the form of tax withholding or estimated tax payments. Due dates and other procedural details vary by jurisdiction, but April 15, Tax Day is the deadline 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.

For federal individual (not corporate) income tax, the average rate paid in 2020 on adjusted gross income (income after deductions) was 13.6%.^[1] However, the tax is progressive, meaning that the tax rate increases with increased income. Over the last 20 years, this has meant that the bottom 50% of taxpayers have always paid less than 5% of the total individual federal income taxes paid, (gradually declining from 5% in 2001 to 2.3% in 2020) with the top 50% of taxpayers consistently paying 95% or more of the tax collected, and the top 1% paying 33% in 2001, increasing to 42% by 2020.^[2]