The two returns are linked, since IL-1040 starts with federal adjusted gross income (AGI). But Illinois applies its own additions, subtractions, exemptions and credits. Taxpayers often copy federal figures across and miss those differences.
This guide covers who must file, how to work through the 2025 instructions, how Illinois calculates tax, where to find official forms, and how to file, pay and amend. Unless noted, "2025" means the return filed in 2026.
Key Takeaways
- Use the current-year IDOR form and instructions, not an old PDF or a prior-year article.
- Filing rules differ for residents, part-year residents, nonresidents and refund-only filers.
- Illinois has a flat 4.95% rate, no standard deduction, and a $2,850 exemption per person for 2025.
- An extension to October 15, 2026 does not extend the April 15 payment deadline.
Who Must File an Illinois IL-1040?
What Form IL-1040 is used for
IL-1040 reports your Illinois income, calculates state tax, claims exemptions and credits, reconciles withholding and estimated payments, and shows a refund or balance due.
It differs from federal Form 1040 in that it begins with federal AGI but then applies Illinois rules. Federal itemized deductions, for example, are not an Illinois subtraction.
Who may need to file
Per IDOR filing requirements, the tests vary by filer type:
| Filer | When to file |
|---|---|
| Full-year resident | You must file federally, or your Illinois base income exceeds your exemption allowance even without a federal requirement |
| Part-year resident | You had income while an Illinois resident, Illinois-source income while a nonresident, or want a refund of Illinois withholding. File IL-1040 with Schedule NR |
| Nonresident | You have Illinois-source taxable income, or need to recover tax withheld in error. File IL-1040 with Schedule NR |
| Resident claimed as a dependent | Your Illinois base income exceeds $2,850, or you want a withholding refund |
A few more situations:
- Refund-only returns. If Illinois withheld tax or you made estimated payments, you must file to get that money back, even if you otherwise wouldn't need to.
- Withheld in error. A nonresident seeking a refund of mistaken withholding needs an explanation letter from the employer.
- Reciprocal states. Residents of Iowa, Kentucky, Michigan and Wisconsin generally owe no Illinois tax on Illinois wages, salaries, tips and commissions.
- Non-wage income. Reciprocity does not cover non-wage Illinois income such as Illinois lottery winnings or Illinois unemployment compensation.
How to Read and Complete the Current-Year IL-1040 Instructions
Before you start
Gather these before entering a single number:
- Your federal return and all W-2s and 1099s
- Illinois withholding records and estimated-payment confirmations
- Your prior-year Illinois return
- Residency move dates, if you moved during the year
- Dependent information and Social Security numbers (or ITINs)
- Receipts for any credits, such as K-12 education expenses
- Bank details for direct deposit
Then confirm the tax year, filing status, names, addresses and spouse and dependent details. For 2025, IDOR requires your full date of birth at Step 1, Line A. Download the form, instruction booklet and schedules from IDOR's current-year forms hub.
Follow the calculation sequence
The 2025 return moves in this order:
- Line 1: federal AGI
- Lines 2 and 3: Illinois additions, giving total income on Line 4
- Lines 5 through 7: subtractions (retirement and Social Security, Illinois refunds, other), totaled on Line 8
- Line 9: Illinois base income
- Lines 10 and 11: exemptions, then net income
- Lines 12 through 19: tax, recapture and credits
- Lines 25 through 31: withholding, payments and refundable credits
- Lines 32 through 41: overpayment, refund choices or amount owed
Line numbers can shift between years, so always check them against the booklet you're using. Transfer federal figures carefully. Not every federal adjustment gets the same treatment in Illinois.
Pick only the schedules that apply
| Schedule | Purpose |
|---|---|
| NR | Nonresident and part-year resident computation |
| IL-WIT | Lists Illinois withholding documents |
| ICR | Property Tax, K-12 Education Expense and Volunteer Emergency Worker credits |
| CR | Credit for tax paid to other states |
| M | Other additions and subtractions (Lines 3 and 7) |
| IL-E/EITC | Dependents, Illinois EITC and Child Tax Credit |
Dependent exemptions are handled in Step 2 and on IL-E/EITC. No separate dependent-exemption schedule exists. Line 25 withholding requires IL-WIT plus the W-2 or 1099 forms showing Illinois income and withholding.
Final review
Before submitting, check:
- Arithmetic and taxpayer identification numbers
- Filing status
- Signatures or e-file authorization
- Bank account and routing numbers
- All required schedules and attachments
- Withholding amounts against your W-2s
- Payment instructions
Applicable nonresident-alien filers must also include a copy of federal Form 1040-NR. Keep a full copy of what you send.
How Illinois Calculates Individual State Income Tax
Rate and tax base
Illinois taxes net income at a flat 4.95% under 35 ILCS 5/201(b)(5.4). There are no brackets.
The path runs from federal AGI to Illinois base income (after additions and subtractions) to net income (after exemptions). The 4.95% applies to that last figure. The federal taxable income number is not the starting point.
Exemptions instead of a standard deduction
Illinois has no standard deduction for individual filers. It uses exemptions instead:
- $2,850 per eligible exemption for 2025, usually $5,700 on a joint return before dependents
- An extra $1,000 for each taxpayer or spouse age 65 or older
- Another $1,000 for each legally blind taxpayer or spouse
- No exemption allowance if federal AGI exceeds $500,000 married filing jointly, or $250,000 for other statuses
The personal exemption rises to $2,925 for 2026. Federal exemptions and deductions don't carry over automatically.
Additions, subtractions and special income
- Retirement and Social Security. Federally taxed Social Security and qualifying employee-plan, IRA and self-employed retirement income in AGI may be subtracted on Line 5.
- Military pay. Qualifying Armed Forces, National Guard and dual-status technician pay is subtracted on Schedule M, Line 21. Attach your W-2; technicians also attach SF-50.
- Investment income. Interest on qualifying U.S. government obligations is exempt. Federally exempt municipal interest generally is not exempt in Illinois.
- Medical debt. New for 2025, Schedule M adds a subtraction for qualifying medical-debt relief included in federal AGI.
Credits and payments
| Credit | Key terms |
|---|---|
| Illinois EITC | 20% of the federal EITC, with expanded eligibility |
| Child Tax Credit | 40% of Illinois EITC; needs a dependent child under 12 on Dec. 31, 2025 |
| Property Tax Credit | 5% of qualifying property taxes; nonrefundable; nonresidents can't claim it |
| K-12 Education Expense | 25% of qualifying expenses above $250, up to $750 |
| Volunteer Emergency Worker | $500 for one awarded taxpayer, $1,000 if both are awarded; IDOR certificate required |
The Property Tax and K-12 credits phase out above the same AGI ceilings as the exemption ($500,000 joint, $250,000 otherwise).
Know the terms. A subtraction lowers income. An exemption lowers net income. A credit lowers tax. Withholding and estimated payments are money already paid, and the difference between your total tax and those payments is your refund or balance due. Keep receipts, property records and withholding statements for any credit you claim.
Official Illinois IL-1040 Forms and Filing Resources
Primary IDOR resources
Start at tax.illinois.gov, using the 2025 Individual Income Tax Forms page. It links the return, instructions, schedules, Spanish-language instructions and 2026 estimated-tax forms. Prior years live in IDOR's archive at taxarchive.illinois.gov.
To confirm a form is current:
- Match the tax-year heading on the hub to the year printed on the document
- Check that the web address is an official tax.illinois.gov page
- Note that the same hub lists both the 2025 return and 2026 estimates, so don't mix them up
Related forms
- IL-1040-X: amended return
- IL-1040-ES: 2026 estimated payments (not for the 2025 return)
- IL-1040-V: payment voucher for 2025 balances
- IL-505-I: calculates and sends tentative tax with an extension
- Schedules NR, IL-WIT, ICR, CR, M and IL-E/EITC: covered above
Where to get help
- Phone: 800-732-8866 or 217-782-3336, Monday to Friday, 8 a.m. to 5 p.m. TTY is 800-544-5304, and telephone translation is available.
- Email: [email protected] for individual inquiries.
- Identity verification: if IDOR sends a letter, you can respond through MyTax Illinois without creating an account.
- Accessibility: [email protected] or 217-524-7003.
Software, paid preparers and advisors offer different levels of support. Before choosing one, confirm it handles your filing status and every schedule you need, such as Schedule NR.
How to File, Pay, Extend and Track an Illinois Return
Filing methods
| Method | Notes |
|---|---|
| MyTax Illinois | Free. Requires full-year Illinois residence, a filed 2024 IL-1040, an SSN or ITIN and a valid email. Handles eligible original returns, not first-time filers |
| Tax software or a professional | Best for part-year, nonresident or multi-schedule returns |
| Paper, no payment | IDOR, PO Box 19041, Springfield IL 62794-9041 |
| Paper, with payment | IDOR, PO Box 19027, Springfield IL 62794-9027 |
The IRS Free File program covers federal returns. Don't assume it includes a free IL-1040; check with IDOR first.
Deadlines, extensions and payments
- Return and payment due: April 15, 2026.
- Automatic filing extension: to October 15, 2026. It does not extend payment.
- IL-505-I: use it to calculate and send tentative tax. It isn't required to get the automatic extension.
- Payment methods: bank account payment through MyTax, credit card online (with a provider convenience fee), or check or money order mailed with IL-1040-V.
- IL-1040-V address: Illinois Department of Revenue, Springfield IL 62726-0001. Don't use the return-mailing address.
Penalties add up. Late payment costs 2% for 1 to 30 days and 10% after 31 days. Interest is 7% simple interest through December 31, 2026. Illinois Pub-103 has the full formulas.
For 2026 estimates, IL-1040-ES applies when expected liability exceeds $1,000. Installments are due April 15, June 15 and September 15, 2026, then January 15, 2027. After paying, confirm the payment has posted to the correct tax year.
Refunds and recordkeeping
Track a refund with Where's My Refund, which updates each business day. IDOR indicates about four weeks for e-filed returns and potentially more than eight weeks for paper. Treat those as estimates.
Save the filed IL-1040, your federal return, all schedules, confirmation numbers, payment receipts and source documents. IRS guidance suggests three years in most cases, with longer periods for substantial income omissions or fraud. That is IRS guidance, not an Illinois-specific rule.
Special Situations, Amendments and Common Filing Errors
Moving, remote work and multiple states
Illinois residency follows domicile, including your intent to return after a temporary absence. Living overseas doesn't automatically end Illinois domicile.
Part-year residents report all income received while resident, plus Illinois-source income received as a nonresident.
If your Illinois W-2 shows wages that should be taxed elsewhere, ask the employer for a letter on letterhead stating the correct wages and workdays in each state. IDOR's 30-working-day withholding rule has conditions, so it isn't a blanket exemption for remote workers.
Schedule CR credits eligible tax paid to another state on income earned during Illinois residence. Nonresidents can't claim it, and foreign-country income taxes don't qualify. Tax withheld by a reciprocal state is recovered from that state, not claimed on CR.
International taxpayers and complex income
Federal resident-alien or nonresident-alien status, Illinois domicile, credit eligibility and MyTax eligibility are all separate tests. One doesn't answer the others.
NRIs, ITIN holders, people with foreign income or employers, and owners of US businesses should get professional review rather than guess.
VJM Global offers remote US tax-compliance and accounting support, including Form 1040-NR preparation, treaty-position disclosures on Form 8833 and withholding management. It serves NRIs, foreign investors and multinational companies with cross-border filing questions. It does not operate an Illinois office.
Amended returns
Use IL-1040-X when a change affects Illinois net income or credits. Common triggers include omitted income, incorrect withholding, missed credits, a federal amendment or an IRS adjustment.
File a separate amendment for each affected year, after a processable original return. Include corrected schedules, explanations and proof of any federal change.
If a federal change increases Illinois tax, file and pay within 120 days of federal finalization. Refund claims tied to a federal change generally have two years plus 120 days from finalization.
Common errors
IDOR's most frequent problems include:
- Confusing the federal and state returns
- Using the wrong tax year
- Copying federal figures without Illinois adjustments
- Omitting Schedule NR or a credit schedule
- Entering incorrect withholding or bank details
- Choosing the wrong filing status or omitting income
- Leaving out signatures or dates
- Sending payment for the wrong period
Frequently Asked Questions
What is Form IL-1040?
IL-1040 is Illinois's individual income tax return. It is separate from federal Form 1040, though it starts with federal AGI. Use the current version from IDOR.
Who has to file an Illinois IL-1040?
Full-year residents, part-year residents, nonresidents with Illinois-source income, and anyone seeking a refund of Illinois withholding or estimated payments. Check IDOR's filing requirements page for current thresholds.
Where can I find current Illinois IL-1040 instructions?
On IDOR's 2025 Individual Income Tax Forms page at tax.illinois.gov. It links the return, instructions, schedules and updates. Prior years are in IDOR's archive.
Does Illinois have a standard deduction?
No. Illinois uses a personal exemption allowance instead: $2,850 per eligible person for 2025, with extra $1,000 amounts for age 65 and over or blindness. Income limits apply.
How do part-year residents and nonresidents file an Illinois return?
They file IL-1040 with Schedule NR to allocate income to Illinois. Residency and income sourcing facts can change whether you must file at all.
How do I amend or pay an Illinois IL-1040?
Amend with IL-1040-X after a processable original return, one form per year. Pay through MyTax, by card, or by check with IL-1040-V. An extension doesn't delay payment.
