Illinois tax filing: file IL state taxes online, Form IL-1040, deadlines and requirements

Do you have to file an Illinois tax return?

Illinois ties its filing requirement to your federal return, then adds a second test for people who did not have to file federally. You must file an IL-1040 for 2025 if either of these is true:

• You were required to file a federal income tax return, or
• You were not required to file federally, but your Illinois base income is greater than your Illinois exemption allowance.

Part-year residents and nonresidents file when they earned enough Illinois-source income to owe tax, and they attach Schedule NR to allocate income between Illinois and everywhere else. Because the first test simply mirrors the federal filing requirement, most working residents who file a 1040 also file an IL-1040.

Reasons to file even when you are not required to

• Illinois withholding on your W-2. If Illinois tax came out of your paychecks and you owe nothing, filing is the only way to recover it.
• The Illinois Earned Income Credit. This refundable credit, now worth 20 percent of the federal EITC, requires a filed return.
• The property tax credit. Homeowners can claim a credit for 5 percent of Illinois property tax paid on their principal residence.

The current instructions are published by the Illinois Department of Revenue.

The flat rate and the personal exemption allowance

Illinois taxes net income at a single flat rate of 4.95 percent for tax year 2025. There are no graduated brackets. A 2020 ballot measure to move Illinois to a graduated tax failed, so the flat rate has held, which makes the math unusually simple: your Illinois base income times 0.0495, less credits.

Illinois has no standard deduction. What reduces your taxable income is the personal exemption allowance, set at $2,850 per person for 2025. You claim it for yourself, your spouse on a joint return, and each dependent. Taxpayers who are 65 or older, or legally blind, claim an additional $1,000 exemption each. The allowance phases out for very high incomes.

Illinois also starts from federal adjusted gross income and then subtracts income it does not tax, most importantly retirement income. Distributions from qualified plans, IRAs, most pensions, and Social Security are subtracted out on Schedule M, so Illinois retirees often owe little or no state tax. That single subtraction is one of the biggest differences between the Illinois return and the federal one. Understanding how the two connect starts with your adjusted gross income.

Illinois tax filing deadline and the automatic extension

Illinois grants an automatic six-month extension to file, and there is nothing to submit to claim it. You do not file a state extension form and you do not need a federal extension first. The filing deadline simply moves from April 15 to October 15, 2026 by default.

The extension covers filing, not payment. If you expect to owe, the balance is due April 15, 2026, and late-payment penalty plus interest run from that date on anything unpaid. To send a payment with an extension, use Form IL-505-I or pay electronically through MyTax Illinois. If you are getting a refund, there is nothing to pay and nothing to file for the extension.

The federal extension is separate and works differently, so review both. Our guide to filing a federal tax extension explains Form 4868, and when taxes are due covers the full 2026 calendar including quarterly estimated payments.

Filing your Illinois return online with TaxFile

Illinois is a straightforward return, but it still draws on your federal figures and its own set of subtractions and credits. TaxFile prepares both from one pass so you are not entering the same W-2 twice.

• Upload or talk. Drop in your W-2s and 1099s and it reads them, or describe your year in plain language and it asks what it still needs.
• Federal and Illinois prepared together. One set of documents produces both returns, with the Illinois figures carried through and retirement income subtracted where it applies.
• Exemptions and credits checked. It applies the personal exemption allowance and looks for the Illinois EITC and property tax credit.
• Error check before anything moves. Inconsistencies are flagged so they are fixed before submission.
• You approve, then it files. E-filing happens through an authorized IRS e-file provider only after you review and approve every line.

Pricing is $39 for a simple return, $89 for self-employed, $199 for business, plus $19 for each state return. There is no free tier. If your Illinois income comes from contract or freelance work, self-employed tax filing covers the Schedule C and Schedule SE side in more detail.

Two limits worth stating plainly. TaxFile does not e-file Form 4868 federal extensions and does not prepare amended returns, and it does not currently handle capital gains on Schedule D, rental income on Schedule E, or cryptocurrency. If your year includes any of those, a CPA is the right call. TaxFile is self-prepared tax software and does not provide personalized tax, legal or accounting advice, and no refund amount is ever guaranteed.