2025 Connecticut State Tax Deadlines

Connecticut Individual Income Tax Filing deadlines and extensions for 2025 for tax professionals to reference when working with clients.

If your client is a resident or has been involved in significant business operations within Connecticut, then they might be required to file Connecticut State Taxes. This document explores the most crucial tax deadlines and tax extensions for Connecticut in 2025.

2025 Connecticut State Tax Deadlines

If your clients are residents or have been involved in significant business operations within Connecticut, then they might be required to file Connecticut State Taxes. This document outlines important tax deadlines and tax extensions for Connecticut in 2025.

Connecticut Business Tax Deadlines for 2025

C Corporation

Connecticut C Corporation Tax Deadlines for 2025
You must file and pay Corporate Income Taxes in Connecticut by May 15, 2026.

• File Online with the Connecticut Department of Revenue Services
• File by Mail must be postmarked by the due date
• Form CT-1120 – Connecticut Corporation Business Tax Return

Extension to File Taxes in Connecticut for 2025
The Extension Deadline for Connecticut corporate tax returns is November 16, 2026.

Connecticut automatically grants a six-month extension for filing corporate income tax returns. This means you do not need to file for an extension in Connecticut.

This is an extension to FILE, not an extension to PAY – payment is still due May 15, 2026.

Pass-Throughs

Connecticut S Corporation & Partnership Tax Deadlines for 2025
You must file in Connecticut by March 16, 2026.

• File Online with the Connecticut Department of Revenue Services
• File by Mail must be postmarked by the due date
• Forms:
  • CT-1065/CT-1120SI – Composite Income Tax Return for S Corporations and Partnerships
  • CT-1065 – Connecticut Partnership Income Tax Return

Extension to File S Corporation & Partnership Taxes in Connecticut for 2025
The Extension Deadline for Connecticut S Corporation and Partnership returns is September 15, 2026.

Connecticut automatically grants a six-month extension for filing pass-through entity tax returns. This means you do not need to file for an extension in Connecticut.

This is an extension to FILE, not an extension to PAY – payment is still due March 16, 2026.

Connecticut Individual Tax Deadlines for 2025

Estimated Tax Deadline for Connecticut 2025
Estimated tax payments are due:

• April 15, 2025
• June 16, 2025
• September 15, 2025
• January 15, 2026

See Form CT-1040ES for the amount to pay with each voucher.

Individual Tax Deadline for Connecticut 2025
You must file and pay Individual Income Taxes in Connecticut by April 15, 2026.

• File Online with the Connecticut Department of Revenue Services
• File by Mail must be postmarked by the due date

Forms:

• Form CT-1040 – Connecticut Resident Income Tax Return
• Form CT-1040NR/PY – Nonresident/Part-Year Resident Tax Return

Extension to File Taxes in Connecticut for 2025
The Extension Deadline for Connecticut individual income tax returns is October 15, 2026.

Connecticut automatically grants a six-month extension for filing personal income taxes. This means you do not need to file for an extension in Connecticut.

This is an extension to FILE, not an extension to PAY – payment is still due April 15, 2026.

Sources

• Connecticut State Government Individual Filing Information
• Corporation Welcome Page

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The material discussed on this page is meant for general illustration and/or informational purposes only and is not to be construed as investment, tax, or legal advice. You must exercise your own independent professional judgment, recognizing that advice should not be based on unreasonable factual or legal assumptions or unreasonably rely upon representations of the client or others. Further, any advice you provide in connection with tax return preparation must comply in full with the requirements of IRS Circular 230.