Illinois tax deadlines in 2026: filing dates and estimated payments
Deadlines that fall in calendar 2026: the 2025 return and the 2026 estimated payments. Different year? See Illinois 2025 →
Illinois deadlines in 2026
| 2025 individual return due | April 15, 2026 |
|---|---|
| Extended filing deadline | October 15, 2026 |
| Payment due | April 15, 2026, extension or not |
| Final 2025 estimated payment | January 15, 2026 |
| 2026 estimated payments | April 15, 2026 · June 15, 2026 · September 15, 2026 · January 15, 2027 |
Conforms to the federal deadline; automatic 6-month extension to October 15.
Illinois estimated tax payments in 2026
You reasonably expect your 2026 Illinois tax liability to exceed $1,000 after subtracting Illinois withholding, pass-through withholding and tax credits.
| Q1 (2026 tax year) | April 15, 2026 |
|---|---|
| Q2 (2026 tax year) | June 15, 2026 |
| Q3 (2026 tax year) | September 15, 2026 |
| Q4 (2026 tax year) | January 15, 2027 |
| Voucher | Form IL-1040-ES |
| Underpayment safe harbor | No late-payment penalty if you pay at least 90% of this year's tax or at least 100% of last year's tax in four equal timely installments. |
| Pay online | mytax.illinois.gov |
Four equal installments, or pay all on April 15, 2026; fiscal-year filers adjust dates. Exceptions: taxpayers 65 or older permanently living in a nursing home, and farmers (2/3 of federal gross income from farming). Illinois has no 110% high-income tier. Pub 105 covers estimated payment requirements.
Source: tax.illinois.gov, read September 3, 2026. “four equal installments that are due on April 15, 2026; June 15, 2026; September 15, 2026; and January 15, 2027.”
All 51 jurisdictions in one table: state estimated tax payment dates for 2026.
Illinois extensions
Every state's rule in one table: which states accept the federal extension in 2026.
| Does Illinois accept the federal extension? | Not needed. The state extends everyone automatically. |
|---|---|
| Original due date | April 15, 2026 |
| Extended due date | October 15, 2026 |
| Payment | Still due April 15, 2026. The extension is to file, not to pay. Extensions do not extend the time to pay; use Form IL-505-I to pay tax owed by April 15, 2026 to avoid penalty and interest. |
| How to get it | Nothing to file; pay any tentative tax with Form IL-505-I or through MyTax Illinois by April 15, 2026. |
IL-505-I is a payment form only.
Source: tax.illinois.gov, read September 3, 2026. “We grant an automatic six-month extension of time to file your return. If you receive a federal extension of more than six months, you are automatically allowed that extension for Illinois.”
Federal deadlines in 2026
| 2025 Form 1040 | April 15, 2026 · extension October 15, 2026 |
|---|---|
| 2025 S-corp (1120-S) & partnership (1065) | March 16, 2026 |
| 2025 C-corp (Form 1120) | April 15, 2026 |
| 2026 federal estimated payments (1040-ES) | April 15, 2026 · June 15, 2026 · September 15, 2026 · January 15, 2027 |
Source: IRS Publication 509 and Form 1040-ES instructions, irs.gov.
Frequently asked questions
When are Illinois state taxes due in 2026?
Your 2025 Illinois individual income tax return is due April 15, 2026. If that date falls on a weekend or legal holiday, the deadline moves to the next business day. An extension moves the filing deadline to October 15, 2026, but any tax owed is still due on the original date.
When are Illinois estimated tax payments due in 2026?
Illinois estimated payments for the 2026 tax year are due April 15, 2026, June 15, 2026, September 15, 2026, January 15, 2027. Use Form IL-1040-ES or pay online. The final installment for 2025 was due January 15, 2026.
Does Illinois accept the federal extension?
Not needed. The state extends everyone automatically. The extended filing deadline is October 15, 2026, and tax is still due by April 15, 2026.
Does a Illinois extension give me more time to pay?
No. An extension extends the time to file, not to pay. To avoid penalties and interest, pay what you expect to owe by April 15, 2026.
Dates are the statutory deadlines that fall in 2026 and move to the next business day when they land on a weekend or holiday. Each section links to the source it was checked against. Always confirm with the Illinois tax agency or the IRS before relying on a date. This is general information, not tax advice.