Illinois business tax extension
Illinois extends Form IL-1120 automatically by 7 months, with no extension request and no federal extension needed. The federal extension is Form 7004, due for calendar-year corporations and for partnerships and S corporations. In general, an extension gives you more time to file, not more time to pay.
Last updated · From Illinois's own forms, instructions and laws, cited below
Does Illinois accept the federal extension?
Illinois extends the return automatically, with no extension request and no federal extension needed.
Illinois's rules for each business return, as its own instructions and laws state them:
Corporations
- Return
- Form IL-1120, Corporation Income and Replacement Tax Return
- Due date
- The federal due date of Form 1120 Calendar-year 2026 returns:
- Extension
- Illinois extends the return automatically, with no extension request and no federal extension needed. Tax years ending June 30 get eight months. If the IRS grants an extension past the Illinois date, Illinois allows the federal extension plus one month; attach a copy of the approved federal extension to Form IL-1120.
- Extension length
- 7 months
- Payment
- The tax is due by the original due date, even with an extension. To pay with the extension: Form IL-1120-V, Payment Voucher for Corporation Income and Replacement Tax, or MyTax Illinois.
S corporations
- Return
- Form IL-1120-ST, Small Business Corporation Replacement Tax Return
- Due date
- The federal due date of Form 1120-S Calendar-year 2026 returns:
- Extension
- Illinois extends the return automatically, with no extension request and no federal extension needed. If the IRS grants an extension past the Illinois date, Illinois allows the federal extension plus one month; attach a copy of the approved federal extension to Form IL-1120-ST.
- Extension length
- 7 months
- Payment
- The tax is due by the original due date, even with an extension. To pay with the extension: Form IL-1120-ST-V, Payment Voucher for Small Business Corporation Replacement Tax, or MyTax Illinois.
Partnerships
- Return
- Form IL-1065, Partnership Replacement Tax Return
- Due date
- The 15th day of the 4th month after the tax year ends (April 15 for a calendar year)
- Extension
- Illinois extends the return automatically, with no extension request and no federal extension needed. If the IRS grants a longer extension, Illinois allows the length the IRS approved; attach a copy of the approved federal extension to Form IL-1065.
- Extension length
- 6 months
- Extended due date
- The 15th day of the 10th month after the tax year ends (October 15 for a calendar year)
- Payment
- The tax is due by the original due date, even with an extension. To pay with the extension: Form IL-1065-V, Payment Voucher for Partnership Replacement Tax, or MyTax Illinois.
Estates and trusts
- Return
- Form IL-1041, Fiduciary Income and Replacement Tax Return
- Due date
- The federal due date of Form 1041 Calendar-year 2026 returns:
- Extension
- Illinois extends the return automatically, with no extension request and no federal extension needed. If the IRS grants a longer extension, Illinois allows the length the IRS approved; attach a copy of the approved federal extension to Form IL-1041.
- Extension length
- 6 months
- Payment
- The tax is due by the original due date, even with an extension. To pay with the extension: Form IL-1041-V, Payment Voucher for Fiduciary Income and Replacement Tax, or MyTax Illinois.
When is the federal business extension due?
Corporations, S corporations, partnerships, multi-member LLCs, estates and trusts extend their federal return with Form 7004, filed by the return's original due date. The extension is automatic: no reason is needed and the IRS doesn't approve it. We e-file it for a flat $9.95. These are the 2027 dates for calendar-year 2026 returns:
| Return | Who files | File the extension by | Extended to |
|---|---|---|---|
| Form 1065 Partnerships & multi-member LLCs, Form 7004 | 6 months | ||
| Form 1120-S S corporations (and LLCs taxed as S corps), Form 7004 | 6 months | ||
| Form 1120 C corporations (and LLCs taxed as C corps), Form 7004 | 6 months | ||
| Form 1041 Estates & trusts, Form 7004 | 5½ months | ||
| Form 990, 990-EZ, 990-PF Tax-exempt organizations & private foundations, Form 8868 | May 15, 2027 is a Saturday | 6 months |
Federal dates follow the IRS rule: a deadline on a weekend or legal holiday moves to the next business day. A fiscal-year business counts from its own year-end; see the fiscal-year deadline guide.
Tax-exempt organizations extend the 990 series with Form 8868, not Form 7004. Each return needs its own extension, so extending a business return does not extend its owners' personal returns.
Does an extension give more time to pay?
No. A federal extension moves the filing deadline only: tax owed is due by the original due date, and the IRS charges interest and the late-payment penalty on anything paid after it. Illinois's instructions say the same for its returns: a Illinois extension doesn't move the payment deadline. More in does an extension give you more time to pay?
Where are Illinois's forms and instructions?
On the Illinois Department of Revenue website, which has the current forms, instructions and online services. The rules on this page are summarized from the sources below. We e-file the federal extension; the Illinois return and any Illinois extension request go to the state.
Illinois extension FAQ
Does Illinois accept the federal business tax extension?
Illinois extends the return automatically, with no extension request and no federal extension needed. The extension is 7 months. Tax years ending June 30 get eight months. If the IRS grants an extension past the Illinois date, Illinois allows the federal extension plus one month; attach a copy of the approved federal extension to Form IL-1120.
When is the Illinois Form IL-1120 due?
The federal due date of Form 1120. For calendar-year 2026 returns, that is Thursday, April 15, 2027.
Does a Illinois extension give more time to pay?
No. The tax is due by the original due date, even with an extension. To pay with the extension: Form IL-1120-V, Payment Voucher for Corporation Income and Replacement Tax, or MyTax Illinois.
Does a Illinois business still need a federal extension?
Yes, to get more time for its federal return: Form 7004, filed by April 15, 2027 for a calendar-year corporation or March 15, 2027 for a partnership or S corporation. Illinois's own extension is automatic.
Sources
- IL-1120 Instructions 2025 (R-07/26), Illinois Department of Revenue (PDF), read
- IL-1120-ST Instructions 2025 (R-07/26), Illinois Department of Revenue (PDF), read
- IL-1065 Instructions 2025 (R-07/26), Illinois Department of Revenue (PDF), read
- IL-1041 Instructions 2025 (R-07/26), Illinois Department of Revenue (PDF), read
- 2025 Corporate Income Tax Forms, read
Filing a federal business extension this season?
Filing for 2026 returns opens in January 2027, when the IRS begins accepting them. Leave your email and we'll send one message when it's live.
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