A tax bracket is a defined range of taxable income to which a specific marginal rate applies. Most countries use between 3 and 9 brackets.

As income rises, each additional amount is taxed at the rate for the bracket it falls into. Portugal has 9 brackets (13%–48%); Germany uses a mathematical formula producing effectively infinite brackets; Ireland operates with just two rates (20% and 40%).

Moving into a higher bracket only increases tax on the portion above the threshold — never on income already taxed in lower brackets.