The state of Illinois automatically grants business tax extension when there is no tax due, and there's no need to file a separate form for the extension. If your business owes tax, pay the tax amount due on or before the deadline to get a 7-month extension.
Due date and Penalty
The due date to pay business income tax and filing the tax return/extension is April 15. In case of late filings, you will incur the Penalty for unpaid tax dues as well as for late filings.
The late payment penalty rate will be
Payment of tax dues
You can choose to make a payment between the Check/Money Order and Electronic payment options. If making payments through Check or Money Order, use the Automatic Extension form Form IL-505-B (Automatic Extension Payment) and mail it to the Illinois Department of Revenue.
To pay electronically, check out the payment options available.
| Tax Type | State Tax Form | Due date (Fiscal year) | Due date (Calendar year) | Extension Period | State Tax payment Form |
| C Corporation | IL-1120 | 15th day of the 4th month | April 15 | 6 months | Form IL-505-B |
| S Corporation | IL-1120-ST | 15th day of the 3rd month | March 16 | 7 months | Form IL-505-B |
| Partnerships | IL- 1065 | 15th day of the 4th month | April 15 | 6 months | Form IL-505-B |
For more information state business tax extension, click here.
