Illinois Income Tax Calculator 2026

Illinois has one of the simplest state income tax systems in the country: a single flat rate applied to nearly all income after personal exemptions. There are no brackets, no graduated rates, and no standard deduction separate from the per-person exemption amount.

The Flat Rate Structure

The Illinois individual income tax rate is 4.95%. This rate is written into the Illinois Constitution and has been in effect since 2011, when it was temporarily raised from 3%, then made permanent at the current level. Because it is a flat rate, every dollar of taxable Illinois income is taxed at exactly the same percentage, whether you earn $10,000 or $10 million.

This makes Illinois different from the federal system and from the majority of US states, which use progressive brackets where higher incomes face higher marginal rates. In practice, the flat rate means your Illinois tax is roughly proportional to your income — the calculation is straightforward enough to do by hand.

Personal Exemptions

Before the flat rate is applied, Illinois allows you to subtract a personal exemption for each person on your return. For 2026, the personal exemption is $2,925.00 per person. You get:

• One exemption for yourself
• One exemption for your spouse if you file a joint return
• One exemption for each dependent you claim

The exemption amount is adjusted annually for inflation by the Illinois Department of Revenue. It has generally increased by small amounts each year. The exemption reduces your taxable income dollar for dollar, which means it is worth exactly $144.79 in tax savings per person at the 4.95% rate.

How the Calculation Works

The Illinois income tax calculation follows a simple formula. Start with your federal adjusted gross income, then apply Illinois-specific additions and subtractions to reach your Illinois base income. Common additions include interest from out-of-state municipal bonds and certain deductions you claimed on your federal return. Common subtractions include Social Security benefits, retirement income up to certain limits, and interest from US government obligations.

From base income, subtract your total personal exemptions to get Illinois net income. Multiply net income by 4.95% to get your gross tax. Then subtract any credits you qualify for — including the property tax credit, earned income credit, and education credits — to arrive at your net Illinois income tax.

The federal income tax and the Illinois income tax operate on fundamentally different principles. Understanding the difference helps you see how each tax affects your total bill and why the two systems behave so differently as your income changes.

Progressive vs Flat

The federal system uses seven progressive tax brackets for 2026, ranging from 10% at the bottom to 37% at the top. As your income rises, each additional dollar is taxed at a higher marginal rate. Your effective rate — total tax divided by total income — is always lower than your top bracket because only the income within each bracket is taxed at that bracket's rate.

Illinois uses a single flat rate of 4.95%. Every dollar of taxable income is taxed at the same rate, so your marginal rate and your effective rate are nearly identical (differing only because of the personal exemption). There is no bracket creep and no cliff where crossing a threshold changes the rate on income you already earned.

Why Your Federal Bill Is Usually Higher

For most Illinois taxpayers, the federal income tax bill is substantially larger than the state tax bill. There are two reasons. First, federal rates are generally higher — the top 4.95% Illinois rate is well below the middle federal brackets. Second, federal tax applies to a broader base after the standard deduction, while Illinois only taxes income after the much smaller personal exemptions.

At $75,000 of income for a single filer, federal tax is roughly four to five times the Illinois tax. At higher incomes, the gap widens further because federal rates climb into the 22%, 24%, and 32% brackets while Illinois stays at 4.95%. The exception is at very low incomes, where federal tax can be zero (due to the standard deduction and credits) while Illinois may still collect something once income exceeds the personal exemption.

What Filing Status Means in Each System

Filing status matters a lot for federal tax because it changes both the standard deduction and every bracket threshold. Married filing jointly gets roughly double the brackets of single, and head of household gets something in between. Your filing status can change your federal tax by thousands of dollars.

In Illinois, filing status only changes the number of personal exemptions you claim. Married filing jointly gets two exemptions instead of one, which is worth $144.79 in tax savings compared with single. Head of household gets the same single exemption as a single filer. There is no separate bracket structure for each status.

Whether you need to file an Illinois Form IL-1040 depends on your residency status, your income, and whether you are required to file a federal return. The rules are simpler than the federal filing requirements because Illinois has fewer filing categories.

Illinois Residents

If you were an Illinois resident for the full year, you generally must file an IL-1040 if:

• You are required to file a federal income tax return
• You had Illinois income tax withheld from your pay and want a refund
• You qualify for refundable credits like the Illinois Earned Income Credit
• You had Illinois estimated tax payments or overpayment credits applied from last year

Even if you are not technically required to file, it is usually a good idea to file if you had any Illinois tax withheld or if you might qualify for refundable credits. You cannot get a refund without filing a return.

Part-Year Residents and Nonresidents

If you moved into or out of Illinois during the year, you file as a part-year resident using Form IL-1040 and Schedule NR. You pay Illinois tax on income you earned while you were a resident, plus any income from Illinois sources while you were a nonresident.

If you were never an Illinois resident but earned income from Illinois sources — for example, if you worked in Illinois but lived in another state — you may need to file Form IL-1040 with Schedule NR as a nonresident. Common Illinois-source income includes wages earned in Illinois, rental income from Illinois property, and business income from Illinois operations.

When Filing Is Optional

If your income is below the filing threshold for your federal return and you had no Illinois tax withheld, you probably do not need to file an Illinois return. For a single person with only wage income below the standard deduction, federal filing is not required, and therefore Illinois filing is also not required.

However, there is no penalty for filing a return when you do not have to. If you are unsure whether you should file, the safest approach is to file anyway — especially if you had any withholding or estimated payments. You will get any overpayment back as a refund.

Important Deadlines

The Illinois individual income tax return is due on the same day as the federal return — typically April 15 of the following year, or the next business day if April 15 falls on a weekend or holiday. If you file for a federal extension, your Illinois filing deadline is automatically extended as well, but you still need to pay any tax you owe by the original deadline to avoid interest and penalties.

While Illinois has a flat tax rate, several credits can reduce your final tax bill dollar for dollar. These are different from deductions and exemptions, which reduce your taxable income — credits directly reduce the tax you owe.

Property Tax Credit

The Illinois property tax credit allows you to claim a credit equal to 5% of the real estate tax you paid on your principal residence during the tax year. The credit applies to property tax paid on your home and up to one acre of land surrounding it. You must have owned and occupied the residence as your principal place of residence. This credit is not refundable, meaning it can only reduce your tax to zero but cannot generate a refund beyond what you paid.

Illinois Earned Income Credit (EIC)

The Illinois Earned Income Credit is a refundable credit equal to 20% of your federal Earned Income Tax Credit. If you qualify for the federal EIC, you automatically qualify for the Illinois version. The credit is fully refundable, meaning it can reduce your tax below zero and generate a refund. For low- and moderate-income working families, the EIC is often the most valuable credit on the Illinois return.

Education Expense Credit

The Illinois education expense credit provides a credit of 25% of qualified K-12 education expenses above $250, up to a maximum credit of $750 per student. Qualified expenses include tuition, books, and lab fees for students in kindergarten through 12th grade at public or private schools. The credit is available regardless of your income level.

Child Tax Credit

Illinois also offers a child tax credit for qualifying children under age 17. The credit amount and income limits vary by year. Check the current IL-1040 instructions for the latest figures. Like the federal child tax credit, it is subject to income phase-outs at higher earnings levels.

Federal tax rates, brackets, and standard deduction amounts for 2026 come from IRS Revenue Procedure 2025-32 (§3.01 tax rate tables, §3.03 maximum capital gains rate, §3.14 standard deduction). Illinois figures use the 4.95% flat rate with $2,925.00 personal exemptions, consistent with the Form IL-1040 instructions and the Illinois Department of Revenue withholding guidance.

Disclaimer: this is a planning tool, not tax advice or a substitute for professional tax preparation or filing software. The calculator estimates federal and Illinois income tax using simplified inputs and does not account for itemized deductions, tax credits, capital gains, retirement contributions, self-employment taxes, or Illinois-specific additions and subtractions to federal AGI. Consult a tax professional for advice tailored to your specific situation.