Connecticut State Tax Guide
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Connecticut State Tax Guide
Extension rules
Extension type: Automatic with Federal · CT-1040 EXT (Application for Extension of Time to File Connecticut Income Tax Return)
If you requested a Federal Extension (Form 4868) AND owe $0 in CT state taxes: You do not need to file a separate state extension form. Connecticut automatically honors your federal extension. If you owe CT state taxes: You must file a state extension and submit your payment by the April deadline to avoid late payment penalties. If you didn’t request a Federal Extension: You must file a Connecticut-specific extension form and show "good cause" for the request.
If you owe tax: If you owe CT state taxes: You must file a state extension and submit your payment by the April deadline to avoid late payment penalties. Any tax due is still due by April 15. Interest begins accruing immediately on unpaid tax after the original due date. You MUST file Form CT-1040 EXT if you owe a tax liability regardless if you filed a federal tax extension.
If you owe $0: If you requested a Federal Extension (Form 4868) AND owe $0 in CT state taxes: You do not need to file a separate state extension form. Connecticut automatically honors your federal extension.
How to request
- Online: Electronic Filing (Highly Recommended): You can request your extension and submit payments directly through the state's official portal: myconneCT.
- Mail: Paper Form: If you prefer to mail your request alongside a physical check, use Form CT-1040 EXT (Application for Extension of Time to File Connecticut Income Tax Return). You can download the official document directly from Form CT-1040 EXT.
You must accurately estimate your tax liability and pay any balance owed by the April deadline. If you do not pay on time, Connecticut will charge a 10% late payment penalty plus interest on the unpaid amount from the original due date until the tax is paid in full. You must pay at least 90% of the total tax shown on your eventual return by April 15, and you can pay the remaining balance when you file the return by October 15.
DRS — Resident income tax information (extension)
Relevant Links
Connecticut Key deadlines (tax year 2025, return filed in 2026)
- Filing deadline: Apr 15, 2026
- Extension request deadline: Apr 15, 2026 — You must file Form CT‑1040 EXT if you: • Did not request an extension of time to file your federal income tax return, but you are requesting an extension of time to file your Connecticut income tax return; or • Have requested an extension of time to file your federal income tax return but you expect to owe additional Connecticut income tax for 2023 and wish to submit a payment with Form CT‑1040 EXT.
- Extended return deadline: Oct 15, 2026 (6-month extension)
- Payment deadline: Apr 15, 2026
- Differs from federal: No
Any tax due is still due by April 15. Interest begins accruing immediately on unpaid tax after the original due date. You MUST file Form CT-1040 EXT if you owe a tax liability regardless if you filed a federal tax extension.
If the due date for filing your return falls on a Saturday, Sunday, or legal holiday, your return is due by the next regular working day.
Estimated payments
- Apr 15, 2026
- Jun 15, 2026
- Sep 15, 2026
- Jan 15, 2027
October 15, 2026 (6-month extension)
Payment rules
You must accurately estimate your tax liability and pay any balance owed by the April deadline. If you do not pay on time, Connecticut will charge a 10% late payment penalty plus interest on the unpaid amount from the original due date until the tax is paid in full. You must pay at least 90% of the total tax shown on your eventual return by April 15, and you can pay the remaining balance when you file the return by October 15.
Official payment portal
Payment options
- myconneCT
- Form CT-1040 EXT
- Form CT-1127 (Application for Extension of Time for Payment of Income Tax)
Payment plan availability
Available: Yes
Short-Term Relief: You can file Form CT-1127 (Application for Extension of Time for Payment of Income Tax) on or before the April deadline to request up to an extra 6 months to pay. However, you must prove undue hardship, provide a statement of assets/liabilities, and show why you cannot borrow the funds. Interest will still accrue. Installment Agreements: Connecticut allows taxpayers to request a formal monthly payment plan. Once your final return is processed and you receive a bill, you can log into the myconneCT to apply for an installment agreement online.
Filing forms
Regular filing
- Form CT-1127 - Application for Extension of Time for Payment of Income Tax
Extension
- Form CT-1040 EXT - Application for Extension of Time to File Connecticut Income Tax Return
Connecticut Refund Tracking
Processing time: Go to Connecticut refund status and select "Where's my Refund?"
Relevant Links
Do I need to file?
If you requested a Federal Extension (Form 4868) AND owe $0 in CT state taxes: You do not need to file a separate state extension form. Connecticut automatically honors your federal extension. If you owe CT state taxes: You must file a state extension and submit your payment by the April deadline to avoid late payment penalties. If you didn’t request a Federal Extension: You must file a Connecticut-specific extension form and show "good cause" for the request.
- Residents: If you requested a Federal Extension (Form 4868) AND owe $0 in CT state taxes: You do not need to file a separate state extension form. Connecticut automatically honors your federal extension.
- Part-year residents: If you owe CT state taxes: You must file a state extension and submit your payment by the April deadline to avoid late payment penalties.
- Nonresidents: If you didn’t request a Federal Extension: You must file a Connecticut-specific extension form and show "good cause" for the request.
Filing methods
Online filing
Electronic Filing (Highly Recommended): You can request your extension and submit payments directly through the state's official portal: myconneCT.
Mail filing
Paper Form: If you prefer to mail your request alongside a physical check, use Form CT-1040 EXT (Application for Extension of Time to File Connecticut Income Tax Return). You can download the official document directly from Form CT-1040 EXT.
