CT-1120 EXT: Application for Extension of Time to File Corporation Business Tax Return (2025)
Connecticut · Connecticut DRS · Used for tax years 2025
Form CT-1120 EXT requests an extension of time to file a 2025 Connecticut Corporation Business Tax Return or Combined Unitary Corporation Business Tax Return. It reports tentative tax, credits, prior payments, and any amount due with the extension request. The extension gives you
Who files this form
Corporations seeking more time to file Connecticut Form CT-1120 or Form CT-1120CU use Form CT-1120 EXT. It requests a six-month filing extension, or a seven-month extension for corporations with a June 30 fiscal year end.
For a combined unitary group, the Designated Taxable Member should file one application for all members included in Form CT-1120CU. Payments should be made under that member’s Connecticut Tax Registration Number.
A federal extension does not replace this application. To get the Connecticut extension, complete the entire form, file it on time, and pay the amount on Line 15.
When it's due
For tax year 2025:
- Calendar-year filers: The application deadline is May 15. The form requests an extension to November 15, 2026.
- Fiscal-year filers: File by the fifteenth day of the month following the due date of the corporation’s corresponding federal income tax return. Enter the fiscal year end and requested extended filing date on the form.
If a due date falls on a Saturday, Sunday, or legal holiday, filing on the next business day is considered timely.
This extension gives you more time to file, not more time to pay. Pay the amount shown on Line 15 with the application.
What you'll need
Have these details ready to complete the application:
- Corporation or Designated Taxable Member name, address, Connecticut Tax Registration Number, and federal Employer Identification Number (FEIN).
- Income-year beginning and ending dates, and the requested extension date for a fiscal-year return.
- Whether federal Form 7004 was filed. If it was not, an explanation of why you are requesting the Connecticut extension.
- Tentative tax, applicable surtax and tax credit recapture, tax credits, estimated tax payments, and prior-year overpayment.
- For combined unitary filers, the number of taxable members and their tax and credit information.
- Corporate officer’s name, title, signature, date, and telephone number. Someone signing instead of an officer must have a signed Power of Attorney.
- If using a paid preparer, the preparer’s signature, date, SSN or PTIN, and firm’s FEIN, along with the other preparer details requested on the form.
Use Form CT-1120K to determine allowable tax credits as directed in the line instructions.
How to file
File electronically
Form CT-1120 EXT must be filed and paid electronically. Use myconneCT at portal.ct.gov/DRS-myconneCT:
- Log in and find your tax account on the Summary screen.
- Select File an Extension.
- Choose your payment method and file Form CT-1120 EXT.
When filing through myconneCT, you must make an electronic payment at that time. You can authorize a withdrawal from a checking or savings account on a date up to the due date, or pay by credit or debit card. Card payments carry a convenience fee. Save the confirmation number and a copy of the return.
Waivers and paper filing
The form warns not to mail a paper return. To request a waiver from electronic filing, visit portal.ct.gov/DRS and complete Form DRS-EWVR, Electronic Filing and Payment Waiver Request.
The printed mail instructions say to use blue or black ink and no staples. If you have received an electronic-payment waiver, make the check payable to Commissioner of Revenue Services. Write “2025 Form CT-1120 EXT” and the corporation’s Connecticut Tax Registration Number on the front. Sign the check and paper clip it to the front of the return. Do not send cash.
Paper return with payment:
Department of Revenue Services
State of Connecticut
PO Box 2974
Hartford CT 06104-2974
Paper return without payment:
Department of Revenue Services
State of Connecticut
PO Box 150406
Hartford CT 06115-0406
Common mistakes
- Treating the extension as extra time to pay. It extends only the filing deadline. Unpaid tax is subject to penalty and interest.
- Submitting an incomplete application. The instructions require the entire form to be completed and Line 15 paid.
- Ignoring electronic filing and payment requirements. The instructions provide a waiver process and warn of penalties for failing to pay electronically.
- Assuming online banking sends an electronic payment. Verify that your financial institution sends an EFT, not a check.
- Using the wrong year’s form. Submit the correct year’s form to avoid processing delays.
- Entering too much PE credit on Line 10. It cannot exceed the balance of tax payable on Line 9.
- Forgetting to keep a copy. The form tells you to retain a copy for your records.
Questions people ask
Do I need to give a reason for requesting the extension?
Not if federal Form 7004 was filed with the IRS. If it was not filed, the corporation may request a Connecticut extension for reasonable cause and must explain the request on the form.
Does a combined unitary group need an application for each member?
The Designated Taxable Member should file one Form CT-1120 EXT for all members included in Form CT-1120CU. An approved filing extension for any member is valid for all members of the group.
Who can sign the application?
A corporate officer must sign. Anyone with a signed Power of Attorney may sign in the officer’s place. A paid preparer must also sign and date the form and provide the required identification numbers.
Can an approved extension help me avoid an underpayment penalty?
If the filing extension is granted, the corporation may avoid the penalty for failing to pay the full amount by the original deadline if it pays at least 90% of the tax shown on the return by that deadline and pays the balance with Form CT-1120 or Form CT-1120CU by the extended deadline. Interest is assessed at 1% per month or fraction of a month on underpaid tax, starting from the return’s due date.