AfterTaxLabFederal income tax
Federal income tax is a mandatory levy imposed by the United States government on the earnings of individuals and businesses. It functions as a progressive tax, meaning tax rates increase as income levels rise across specific brackets. This tax measures a portion of your annual compensation paid to the Internal Revenue Service to fund public services, national defense, and infrastructure projects.
Federal income tax, in plain terms
This tax is distinct from payroll taxes like Social Security or Medicare, which are flat-rate contributions earmarked for specific social insurance programs. Federal income tax is not a fixed fee but a variable amount determined by your total annual income and filing status. It is separate from state or local income taxes, which are assessed independently by regional governments.
Federal income tax on a real salary
Every figure below is produced by the same engine that runs the AfterTaxLab calculators — nothing here is estimated by hand.
| Item | 2026 figure |
|---|---|
| Gross salary (example, single filer) | $100,000 |
| Taxable income after the standard deduction | $83,900 |
| Federal income tax | $13,170 |
| Marginal bracket at that salary | 22% |
| Effective federal rate | 13.17% |
The calculation process begins by subtracting the standard deduction from gross pay to determine taxable income. In the provided example, taxable income is $83,900. While the total federal income tax owed equals $13,170, this amount is determined by applying progressive rates to portions of that income. The final dollar of the salary is taxed at a marginal rate of 22%.
Using federal income tax on AfterTaxLab
Federal income tax is a primary component of the take-home pay calculation available on the AfterTaxLab main dashboard. When you input your annual salary and filing status, the calculator automatically deducts this amount from your gross pay. Look for the federal tax line item in the summary table to see how much is withheld from your paycheck.
Federal income tax: common questions
Is federal income tax the same as my total tax withholding?
No. Federal income tax is just one part of your total withholding. Your paystub also includes mandatory payroll taxes for Social Security and Medicare. These specific contributions are separate from the $13,170 federal income tax figure and are calculated using different statutory rates regardless of your tax bracket.
Why does my marginal tax rate differ from my effective tax rate?
Your marginal rate applies only to the last dollar earned, which in this example is 22%. The effective rate, such as 13.17%, represents the actual percentage of your total income paid to the government after applying progressive brackets and deductions to your entire gross salary.
How does the standard deduction lower my federal income tax?
The standard deduction reduces the amount of your gross pay that is subject to federal income tax. By subtracting this amount, you arrive at a lower taxable income of $83,900. This process ensures that a portion of your earnings remains completely exempt from federal taxation each year.
Figures calculated with the AfterTaxLab 2026 engine: federal brackets and standard deduction ($16,100 single), Social Security wage base $184,500, published 2026 state rates. Estimates for planning only — not tax advice. Last verified 21 Sep 2026 · methodology.
Marginal rate vs effective rate: why your last dollar is not your tax rate
The 2026 single brackets run 10%, 12%, 22%, 24%, 32%, 35% and 37%, and each rate applies only to the slice of taxable income inside its own band: the first $12,400 is taxed at 10%, the next slice at 12%, and so on up to $640,600. That is why the worked example on this page owes $13,170 on $100,000 of gross salary — an effective federal rate of 13.17% — even though its final dollar falls in the 22% bracket. The 22% is a marginal rate; the 13.17% is the average across the slices that were actually taxed.
The distinction matters whenever you compare two salaries or plan a raise. Moving into a higher bracket never reduces take-home pay, because only the dollars above the threshold are taxed at the higher rate. It does mean each extra dollar is worth slightly less than the dollar before it, which is why a large raise usually adds less to a paycheck than a simple percentage suggests.
What changes the number
- Filing status: the standard deduction is 16,100 for a single filer and 32,200 for a married couple filing jointly, and the bracket thresholds shift with it.
- Pre-tax contributions: 401(k) deferrals, traditional IRA and HSA contributions lower taxable income before the brackets are applied.
- Credits and dependents: credits reduce the tax itself, while dependents and filing status change which bands your income falls into.
- Other income: interest, dividends, capital gains and self-employment profit follow their own rules rather than the ordinary wage brackets.
Not every worker owes federal income tax. When the standard deduction and other adjustments push taxable income to the bottom of the first bracket, the federal income tax line can be zero — but Social Security and Medicare are payroll taxes rather than income tax, and they still apply to wages. Federal income tax is also separate from state income tax, which is why the same salary can produce very different take-home pay in two neighbouring states.