What Is Income Tax?
Definition
Income Tax: The tax on the earnings and income of individuals in one calendar year: wages, rent, self-employment and business income. Many countries set it with a progressive tariff of brackets and rates.
Income tax is the tax on what a person earns in one calendar year: wages, rent, self-employment and business income. Many countries set it with a progressive tariff: the taxable income is split into brackets, and each bracket has its own rate. A larger taxable income reaches higher brackets and higher rates.
Where it appears in the formulas
The tax is the sum, over the brackets, of the part of the taxable income in each bracket times that bracket’s rate: tax = Σ (amount in bracket × bracket rate). The income tax calculator shows this bracket by bracket for a yearly taxable income. The gross-to-net salary calculator applies the same tariff to the cumulative base of a wage.
In Türkiye
Income Tax Law no. 193 sets income tax with the progressive tariff of article 103. In 2026 the tariff rates are 15%, 20%, 27%, 35% and 40%.