Delaware Filing Due Date: Corporate income tax returns are due by April 15th— or by the 15th day of the 4th month following the end of the taxable year (for fiscal year filers). Partnership tax returns are due by March 15th — or by the 15th day of the 3rd month following the end of the taxable year (for fiscal year filers).
Extended Deadline with Delaware Tax Extension: Delaware offers a 6-month extension for corporations, which moves the filing deadline to October 15th (for calendar year taxpayers). For partnerships, a Delaware extension will cover the same period of time as the Federal extension (IRS Form 7004), for which the extended deadline is September 15.
Delaware Tax Extension Form: C corporations should use Form 1100-EXT to request a Delaware extension. S corporations should use Form 1100S-EXT to request a Delaware extension. Partnerships must file a copy of their approved Federal tax extension with the Delaware Division of Revenue in order to obtain a state extension. Your Delaware extension request must be filed by the original deadline of your return.
Delaware Extension Payment Requirement: An extension of time to file is not an extension of time to pay. If you owe Delaware tax, your balance must be paid by the original due date to avoid interest and penalties. C corporations can make a Delaware extension payment with Form 1100T-EXT. S corporations can make an extension payment with Form 1100P-EXT. State tax payments can also be made electronically via Delaware’s Online Services portal: revenue.delaware.gov/services/online
Delaware Tax Extension Tips: If you have a 6-month Federal tax extension (IRS Form 7004), the State of Delaware will automatically grant you a 6-month Delaware extension. In this case, you do not need to file a separate state extension application. Make sure to attach a copy of your approved Federal extension to your Delaware return when you file.
Delaware State Income Tax Extension Forms
Website: Delaware Division of Revenue
Form 1100-EXT (Corporation Income Tax Request for Extension): revenue.delaware.gov/current_bt/14_1100_ext.pdf
Form 1100S-EXT (S Corporation Income Tax Request for Extension): revenue.delaware.gov/current_bt/14_1100s_ext.pdf
Form 1100-T-EXT (Delaware Corporate Income Tax Request for Extension, Voucher T-5): revenue.delaware.gov/current_bt/14_1100T-EXT.pdf
Form 1100-P-EXT (Delaware “S” Corporation Request for Extension, Voucher P-5): revenue.delaware.gov/current_bt/14_1100P-EXT.pdf