Corporations doing business in Connecticut that need additional time to prepare their Connecticut Corporation Business Tax Return (Form CT-1120) or Combined Unitary Corporation Business Tax Return (Form CT-1120CU) can file extension Form CT-1120 EXT.
This guide explains the purpose, filing deadlines, step-by-step completion process, electronic filing requirements, and mailing instructions for Form CT-1120 EXT.
What Is the Purpose of Form CT-1120 EXT?
Form CT-1120 EXT, officially titled Application for Extension of Time to File Connecticut Corporation Business Tax Return, allows corporations to request extra time to file their Connecticut business tax returns.
It provides:
- A six-month extension for most corporations.
- A seven-month extension for corporations with a June 30 fiscal year-end.
You do not need to provide a reason for requesting a Connecticut extension if you’ve already filed federal Form 7004 (Application for Automatic Extension of Time to File Certain Business Income Tax, Information, and Other Returns) with the IRS.
If federal Form 7004 was not filed, the corporation may still apply for an extension if it has reasonable cause for the request.
When Is the Deadline to file Form CT-1120 EXT?
Form CT-1120 EXT must be filed on or before the fifteenth (15th) day of the month following the due date of the corporation’s corresponding federal income tax return.
For calendar-year corporations, the due date is May 15.
To receive an approved extension:
- The form must be filed on or before the due date, and
- The corporation must pay the full amount due (Line 15) by that date.
Remember — this form extends only the time to file, not the time to pay taxes owed.
How to Complete Form CT-1120 EXT?
Below is a simplified line-by-line walkthrough of how to correctly complete Form CT-1120 EXT:
Basic Information
- Corporation Name and Address: Enter the exact legal name and mailing address as registered with the Connecticut Department of Revenue Services (DRS).
- Connecticut Tax Registration Number: Include your 10-digit state registration number.
- Federal Employer Identification Number (FEIN): Enter your FEIN as issued by the IRS.
- Income Year Beginning/Ending Dates: Provide the starting and ending dates of your fiscal or calendar year.
Part 1 – Reason for Extension
You generally do not need to explain your reason if a federal extension (Form 7004) was filed.
If not, briefly describe your reasonable cause (for example, awaiting federal K-1 information, delayed accounting finalization, etc.).
Part 2 – Computation of Tax Payment
This section determines the amount due when requesting the extension:
| Line | Description | Instructions |
| 1 | Connecticut Corporation Business Tax Liability | Enter the total estimated tax for the year. |
| 2 | Estimated Tax Payments Made | Include all payments made for the current year. |
| 3 | Credit from Prior Year | Add any overpayments or credits applied from the previous year. |
| 4 | Total Payments and Credits | Add Lines 2 and 3. |
| 5 | Tax Due (if any) | Subtract Line 4 from Line 1. |
| 6–14 | Other applicable adjustments (if indicated on the form). Ensure accuracy based on DRS instructions. |
Line 15: This is the total payment due. You must pay this amount in full when filing Form CT-1120 EXT to avoid interest and penalties.
Electronic Filing Requirements for Form CT-1120 EXT
The Connecticut Department of Revenue Services (DRS) mandates that corporations file and pay electronically. This includes:
- Form CT-1120
- Form CT-1120CU
- Estimated tax payments (Forms CT-1120 ESA, ESB, ESC, and ESD)
- Extension requests (Form CT-1120 EXT)
How to File and Pay Form CT 1120-EXT Electronically?
You must file Form CT-1120 EXT using myconneCT, Connecticut’s online tax portal:
🔗 portal.ct.gov/DRS-myconneCT
- Log in to your myconneCT account.
- Locate your business tax account on the Summary screen.
- Select “File an Extension.”
- Choose your payment method (Direct Payment or Credit/Debit Card).
- File and submit
Payment Options:
- Direct Payment: Authorize DRS to withdraw funds directly from your bank account.
- Credit/Debit Card: Accepted via American Express®, Discover®, MasterCard®, or VISA®. (A small convenience fee applies.)
Important: Payments must be initiated by the due date to avoid penalties and interest.
Penalties for Not Paying Electronically
Failure to remit payments electronically can result in the following penalties:
- First offense: 10% of the tax payment (maximum $2,500)
- Second offense: 10% (maximum $10,000)
- Third and subsequent offenses: 10% penalty
If you cannot comply, you may request a waiver using Form DRS-EWVR (Electronic Filing and Payment Waiver Request) available at portal.ct.gov/DRS.
Where to Mail Form CT-1120 EXT?
If you received a waiver from the e-filing requirement, you may file by mail.
Mail your completed Form CT-1120 EXT using the correct address below:
If payment is enclosed:
Department of Revenue ServicesState of Connecticut
PO Box 2974
Hartford, CT 06104-2974
If no payment is enclosed:
Department of Revenue ServicesState of Connecticut
PO Box 150406
Hartford, CT 06115-0406
Mailing Tips:
- Use blue or black ink only.
- Do not use staples.
- Paper clip your check to the front of the return.
- Write “Form CT-1120 EXT” and your Connecticut Tax Registration Number on the check.
What are the Penalties for filing Connecticut Tax Return Late?
- Interest: 1% per month (or part of a month) on any unpaid tax after the original due date.
- Penalty:
- 10% of unpaid tax or $50 (whichever is greater).
- $50 penalty may apply for late filing even if no tax is due.
To avoid penalties, corporations must pay at least 90% of the total tax due by the original due date and the balance by the extended due date.
FAQs About Form CT-1120 EXT
All C corporations and combined unitary groups operating in Connecticut that require more time to file Form CT-1120 or Form CT-1120CU.
No. It only extends your filing deadline. All taxes must be paid by the original due date.
Yes, if you have reasonable cause for requesting an extension. However, federal Form 7004 automatically supports your Connecticut extension.
Any overpayment will be credited or refunded after your final return (Form CT-1120 or CT-1120CU) is processed.
Upon filing in myconneCT, you will receive a confirmation number for your records.
A surtax is an additional tax imposed on top of the base corporation business tax. In Connecticut, corporations may be subject to a 10% surtax (or as specified by DRS for the current tax year). This surtax applies to the calculated corporation business tax liability before credits, unless an exemption applies.
Tax credit recapture occurs when a corporation previously claimed a credit (such as an investment or job creation credit) but fails to maintain the qualifying activity for the required period. In such cases, the state may recapture part or all of the previously claimed credit, increasing your current year’s tax liability.
No. Only the designated taxable member files Form CT-1120 EXT for the entire combined or unitary group.
Final Thoughts
Filing Form CT-1120 EXT gives Connecticut corporations the extra time they need to prepare accurate business tax returns while avoiding late filing penalties. Remember, this extension only delays the filing deadline, not the payment due date. For corporations with multiple affiliates or unitary structures, ensure that the designated taxable member files the group’s extension and remits payment electronically through myconneCT.
By following the correct procedures — filing on time, paying electronically, and keeping detailed records. you’ll stay fully compliant with Connecticut’s business tax regulations and avoid unnecessary penalties.
