State of Connecticut
Business Income Tax Extensions

Connecticut Filing Due Date: Corporation business tax returns are due on the 15th day of the month following the due date of the equivalent Federal return (for fiscal year filers) or May 15th for C-corps and April 15th for S-corps.

Extended Deadline with Connecticut Tax Extension: Connecticut offers a 6-month extension, which moves the filing deadline to October 1 (for calendar year filers).

Connecticut Tax Extension Form: Use Form CT-1120 to apply for a Connecticut extension. This form can be filed by paper mail or online via Connecticut’s Taxpayer Service Center (TSC). 

Connecticut Extension Payment Requirement: An extension of time to file is not an extension of time to pay. If you owe Connecticut tax, it must be paid by the original due date to avoid penalties and interest. You can mail your extension payment with Form CT-1120, or you can pay electronically through the Taxpayer Service Center (TSC).

Connecticut Tax Extension Tip: If you have filed a Federal tax extension, you do not have to give a reason for needing the Connecticut tax extension. But if you don’t have a valid Federal extension, you are required to provide “reasonable cause” for requesting an extension for your Connecticut return.