An income tax is a tax imposed on individuals or entities (taxpayers) in respect of the income or profits earned by them (commonly called taxable income). Income tax generally is computed as the product of a tax rate times the taxable income. Taxation rates may vary by type or characteristics of the taxpayer and the type of income.

The tax rate may increase as taxable income increases (referred to as graduated or progressive tax rates). The tax imposed on companies is usually known as corporate tax and is commonly levied at a flat rate. Individual income is often taxed at progressive rates where the tax rate applied to each additional unit of income increases (e.g., the first $10,000 of income taxed at 0%, the next $10,000 taxed at 1%, etc.). Most jurisdictions exempt local charitable organizations from tax. Income from investments may be taxed at different (generally lower) rates than other types of 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.

Taxable income of taxpayers resident in the jurisdiction is generally total income less income producing expenses and other deductions. Generally, only net gain from the sale of property, including goods held for sale, is included in income. The income of a corporation's shareholders usually includes distributions of profits from the corporation. Deductions typically include all income-producing or business expenses including an allowance for recovery of costs of business assets. Many jurisdictions allow notional deductions for individuals and may allow deduction of some personal expenses. Most jurisdictions either do not tax income earned outside the jurisdiction or allow a credit for taxes paid to other jurisdictions on such income. Nonresidents are taxed only on certain types of income from sources within the jurisdictions, with few exceptions.

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-time for individuals. Taxable income of taxpayers resident in the jurisdiction is generally total income less income producing expenses and other deductions. Generally, only net gain from the sale of property, including goods held for sale, is included in income. The income of a corporation's shareholders usually includes distributions of profits from the corporation. Deductions typically include all income-producing or business expenses including an allowance for recovery of costs of business assets. Many jurisdictions allow notional deductions for individuals and may allow deduction of some personal expenses. Most jurisdictions either do not tax income earned outside the jurisdiction or allow a credit for taxes paid to other jurisdictions on such income. Nonresidents are taxed only on certain types of income from sources within the jurisdictions, with few exceptions.