Illinois Tax Calculator

Background.

Illinois taxes personal income at a single rate. Since July 2017 every dollar of an individual's Illinois net income has been taxed at 4.95%, whether the filer earns $30,000 or $3 million, because the state constitution requires a non-graduated income tax. A 2020 ballot amendment that would have allowed graduated brackets was rejected by voters. That makes Illinois one of the simpler states to estimate: there is no bracket table to work through and no city or county income tax stacked on top.

A flat rate does not mean the bill is 4.95% of your salary. The Illinois return starts from federal adjusted gross income, applies the state's additions and subtractions, and then takes off an exemption allowance for you, a spouse and any dependants before the rate is applied. Retirement income, including Social Security and qualified pension and IRA distributions, is subtracted altogether, which is why many retirees owe little or nothing. Credits, such as the one for property tax paid on a main home, then come off the tax itself.

So the page asks for the two numbers that matter: the income to tax and the rate to apply. Enter Illinois net income with 4.95% and you get the liability before credits. Enter gross wages at 4.95% and you will overstate it a little, since nothing has been taken off for exemptions; if you know what share of your income went to Illinois tax last year, that effective rate gives a closer estimate. On $100,000 at the statutory rate the tax is $4,950.

The after-tax figure removes only this state tax. Federal income tax, Social Security and Medicare still come out of the same pay.

What is illinois tax calculator?

Illinois individual income tax is a flat percentage of Illinois net income, meaning federal adjusted gross income after the state's additions, subtractions and exemption allowance. The statutory rate for individuals, trusts and estates is 4.95%, which is the default here. The page applies that rate, or any effective rate you type in, to the income you enter and shows what remains after this one tax. It does not prepare a return or work out deductions.

How to use this calculator.

1. 01In Taxable income, enter the Illinois net income your rate applies to if you have last year's IL-1040 to hand; otherwise start from federal adjusted gross income and leave out any Social Security or retirement distributions Illinois exempts.
2. 02Keep the rate at 4.95% when your income figure is already Illinois net income. Enter a lower effective rate if you are working from gross pay and want to allow roughly for exemptions and credits.
3. 03Use whatever period suits you, a year, a month or a single paycheck. The tax is a straight percentage, so both results come out for the same period as the income.
4. 04Treat Income after this tax estimate as a partial figure: subtract federal income tax, Social Security and Medicare separately to get take-home pay.

The formula.

Tax = taxable income × rate ÷ 100, and income after tax = taxable income − tax. There is no bracket schedule, phase-in or minimum. A flat rate means the tax rises in exact proportion to income, so every extra $1,000 adds $49.50 at 4.95%, whether it is the first thousand or the thousandth. The rate field is left open rather than hard-wired so you can model your own effective rate, check an older year (the rate was 3.75% from 2015 until the end of June 2017) or test what a proposed change would cost. What the formula leaves out is everything Illinois does before and after the multiplication: the modifications to federal AGI, the exemption allowance and the credits. Those steps explain the gap between the statutory 4.95% and the share of gross income a household actually pays.

A worked example.

Frequently asked questions.

References& sources.

1. [1]U.S. Internal Revenue Service. Tax guidance current 2026. Official forms, instructions and tax topics. Retrieved 2026-08-06.
2. [2]OpenStax, Rice University. Principles of Finance, 2022. Chapters 6–10. Retrieved 2026-08-06.
3. [3]U.S. Securities and Exchange Commission. Investor.gov current 2026. Investment products and risk. Retrieved 2026-08-06.