A pay stub usually shows at least three federal lines: federal income tax, Social Security, and Medicare. They are calculated differently, and a raise does not move all three the same way.
Income tax uses brackets
Federal income tax is applied to taxable wages after the standard deduction for 2026. Takehome uses the deduction for single, married filing jointly, married filing separately, or head of household. The part of income inside each bracket is taxed at that bracket’s rate. Only the dollars above a threshold are taxed at the next rate. Being “in” the 22 percent bracket does not mean the whole paycheck is taxed at 22 percent.
The calculator does not itemize deductions and does not apply credits such as the child tax credit. If those matter in your household, the real withholding can be lower than this estimate.
FICA is a separate set of taxes
Social Security is 6.2 percent of wages that count for FICA, and it stops for the year after wages pass the Social Security wage base. Medicare is 1.45 percent and does not stop. An additional Medicare tax of 0.9 percent applies only after wages pass a threshold that depends on filing status. A traditional 401(k) deferral lowers income tax in this estimate, but it does not lower Social Security or Medicare. Pre-tax health premiums do lower the FICA wage base here.
Employers pay their own share of Social Security and Medicare. That share never appears in take-home pay, so it is not shown.