Illinois tax deadlines in 2027: filing dates and estimated payments
Deadlines that fall in calendar 2027: the 2026 return and the 2027 estimated payments. Different year? See Illinois 2025 →
Illinois deadlines in 2027
| 2026 individual return due | April 15, 2027 |
|---|---|
| Extended filing deadline | October 15, 2027 |
| Payment due | April 15, 2027, extension or not |
| Final 2026 estimated payment | January 15, 2027 |
| 2027 estimated payments | April 15, 2027 · June 15, 2027 · September 15, 2027 · January 15, 2028 |
Conforms to the federal deadline; automatic 6-month extension to October 15.
Illinois estimated tax payments in 2027
Illinois estimated payments for the 2027 tax year follow the standard schedule: April 15, 2027, June 15, 2027, September 15, 2027, January 15, 2028. Confirm the current-year voucher and any state-specific threshold with the Illinois tax agency.
Source: tax.illinois.gov.
Illinois extensions
An extension moves the Illinois filing deadline to October 15, 2027. It does not move the payment date: pay what you expect to owe by April 15, 2027. Confirm with the Illinois tax agency whether the federal extension is honored automatically or a state form is required.
Federal deadlines in 2027
| 2026 Form 1040 | April 15, 2027 · extension October 15, 2027 |
|---|---|
| 2026 S-corp (1120-S) & partnership (1065) | March 15, 2027 |
| 2026 C-corp (Form 1120) | April 15, 2027 |
| 2027 federal estimated payments (1040-ES) | April 15, 2027 · June 15, 2027 · September 15, 2027 · January 18, 2028 |
Source: IRS Publication 509 and Form 1040-ES instructions, irs.gov.
Frequently asked questions
When are Illinois state taxes due in 2027?
Your 2026 Illinois individual income tax return is due April 15, 2027. 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, 2027, but any tax owed is still due on the original date.
When are Illinois estimated tax payments due in 2027?
Illinois estimated payments for the 2027 tax year are due April 15, 2027, June 15, 2027, September 15, 2027, January 15, 2028. The final installment for 2026 was due January 15, 2027.
Does Illinois accept the federal extension?
An extension moves the Illinois filing deadline to October 15, 2027. It does not extend the time to pay: pay what you expect to owe by April 15, 2027 to avoid penalties and interest.
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, 2027.
Dates are the statutory deadlines that fall in 2027 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.