An income tax is a government levy (tax) imposed on individuals or entities (taxpayers) that varies with the income or profits (taxable income) of the taxpayer. Details vary widely by jurisdiction. Many jurisdictions refer to income tax on business entities as companies tax or corporation tax. Partnerships generally are not taxed; rather, the partners are taxed on their share of partnership items. Tax may be imposed by both a country and subdivisions. Most jurisdictions exempt locally organized charitable organizations from tax.

Income tax generally is computed as the product of a tax rate times taxable income. The tax rate may increase as taxable income increases (referred to as graduated rates). Tax rates may vary by type or characteristics of the taxpayer. Capital gains may be taxed at different rates than other income. Credits of various sorts may be allowed that reduce tax. Some jurisdictions impose the higher of an income tax or a tax on an alternative base or measure of income.

Most jurisdictions require self-assessment of the tax and require payers of some types of income to withhold tax from those payments. Advance payments of tax by taxpayers may be required. Taxpayers not timely paying tax owed are generally subject to significant penalties, which may include jail for individuals or revocation of an entity's legal existence.