A tax bracket is a slice of income taxed at one rate. The federal system has seven: 10%, 12%, 22%, 24%, 32%, 35%, and 37%. Each applies to a range of taxable income, and the ranges depend on filing status. Income fills the brackets from the bottom up, like water filling a set of stacked containers, and each container is taxed at its own rate.
This is the part people get wrong. Being in the 24% bracket does not mean 24% of your income goes to federal tax. It means the dollars that spilled into that bracket are taxed at 24%. The dollars below were taxed at 10%, 12%, and 22%. Crossing into a higher bracket by one dollar changes the tax on that one dollar, not on everything.
Brackets apply to taxable income, which is gross income minus deductions. A single filer earning $100,000 who takes the standard deduction of $16,100 (2026) has $83,900 of taxable income, and that is the figure that gets sorted into brackets. Contributions to a traditional 401(k) or HSA lower taxable income too, which can pull dollars out of a higher bracket.
The common mistake is turning down a raise, overtime, or a bonus for fear of the bracket. A second one is ignoring state brackets, which add anywhere from 0% to over 13% on top. Bracket thresholds shift each year for inflation, so a figure from last year's return is close but not exact.