How the Federal Income Tax Calculator Works
The US federal income tax system uses a progressive tax structure, meaning higher portions of your income are taxed at higher rates. Your tax is calculated by applying each rate only to the income that falls within that bracket, not your entire income.
First, the calculator determines your Adjusted Gross Income (AGI) by subtracting above-the-line deductions like 401(k) and HSA contributions. Then it applies either the standard deduction or your itemized deductions to arrive at taxable income.
Your effective tax rate is the actual percentage of your total income paid in taxes, which is always lower than your marginal rate. Your marginal rate is the rate applied to your next dollar of income.
Frequently Asked Questions
What is the difference between marginal and effective tax rate?
Your marginal rate is the bracket your last dollar falls into, while your effective rate is your total tax divided by total income. Because of the progressive system, your effective rate is always lower than your marginal rate.
Should I take the standard deduction or itemize?
Take whichever is larger. Most taxpayers benefit from the standard deduction. Itemizing is usually better if your combined mortgage interest, state taxes (capped at $10,000), and charitable donations exceed the standard deduction amount.
Are 401(k) contributions tax-deductible?
Traditional 401(k) contributions are made pre-tax, reducing your taxable income for the year. Roth 401(k) contributions are made after-tax and do not reduce your current year tax liability.
Does this calculator include state taxes?
No, this calculator estimates federal income tax only. State income tax rates vary widely and should be calculated separately using our State Income Tax Calculator.
How accurate is this calculator?
This calculator provides a reasonable estimate based on standard brackets and deductions. Your actual tax may differ due to credits, alternative minimum tax, additional income types, or other factors not captured here.