The US federal income tax is progressive: income is taxed in brackets, with each slice of income taxed at its own rate. For a single filer in 2025, the first $11,925 is taxed at 10%, the slice from $11,926 to $48,475 at 12%, the next slice at 22%, and so on up through 37% at the top. Crucially, earning enough to enter a higher bracket never taxes your earlier dollars more — only the income inside each bracket gets that bracket's rate. The 'my raise pushed me into a higher bracket so I take home less' fear is a pure myth; a raise always increases take-home pay, because the higher rate touches only the dollars above the threshold.
Two numbers describe any tax situation: the marginal rate (the rate on your last dollar, which governs decisions like overtime, bonuses, or extra freelance income) and the effective rate (total tax divided by total income — always lower than the marginal rate under a progressive system). Confusing the two leads to bad decisions, like turning down paid work because 'it'll all go to taxes.' This estimator applies the federal brackets to taxable income; remember that the standard deduction ($15,000 for single filers in 2025) is subtracted from gross income before brackets apply, and state income taxes are entirely separate — nine states have none, while California's top rate exceeds 13%. Brackets adjust yearly for inflation, so always confirm the current year's figures with the IRS rather than relying on last year's numbers.