Connecticut Business Tax Extension 2026: 2025 Tax-Year Filing Guide
LLC & Partnership · S Corporation · C Corporation · Fiduciary
This guide explains how to file a Connecticut (CT) business tax extension for each entity type. If you also need the federal filing step, see our IRS Form 7004 guide. Connecticut extensions vary by entity and generally require the appropriate Connecticut extension form; a federal extension alone may not satisfy every state requirement. However, estimated tax remains due by the original deadline.
Need a pro? Connect with a U.S.-based CPA or EA to prepare and file your CT return.
Remember, payment is still due by the original deadline. In other words, extensions only extend filing time.
Connecticut (CT) rules depend on entity type. Next, confirm the entity’s classification, file the required extension or retain federal proof when applicable, and pay required tax by the original deadline.
Connecticut LLC Tax Extension: Filing Details
A calendar-year partnership or LLC taxed as a partnership generally files Forms CT-1065 and CT-1120SI, as applicable, when a Connecticut filing obligation applies. For the 2025 calendar-year return, the extended filing deadline is September 15, 2026.
In addition, the extension applies to filing time only. Therefore, pay required Connecticut tax by the original deadline to limit penalties and interest.
The extension applies to filing time only. Pay required Connecticut tax by the original deadline to limit penalties and interest.
Connecticut S Corporation Tax Extension: Filing Details
For an S corporation, a calendar-year business generally files Forms CT-1065 and CT-1120SI, as applicable, when a Connecticut filing obligation applies. For the 2025 calendar-year return, the extended filing deadline is September 15, 2026.
Connecticut C Corporation Tax Extension: Filing Details
For a C corporation, a calendar-year business generally files Forms CT-1120 and CT-1120CU, as applicable, when a Connecticut filing obligation applies. For the 2025 calendar-year return, the extended filing deadline is November 16, 2026.
The extension applies to filing time only. Pay required Connecticut tax by the original deadline to limit penalties and interest.
The extension applies to filing time only. Pay required Connecticut tax by the original deadline to limit penalties and interest.
Fiduciary, Estate, and Trust Filing Details
Finally, a calendar-year estate or trust generally files Form CT-1041, as applicable, when a Connecticut filing obligation applies. For the 2025 calendar-year return, the extended filing deadline is September 30, 2026.
Quick Reference: Deadlines and Forms
The table below provides a quick reference to Connecticut business tax extensions. For broader filing context, visit our business tax extension resource.
| Entity Type | CT Return Form | Extension Method | Extended Deadline |
|---|---|---|---|
| LLC / Partnership | CT-1065/CT-1120SI | CT-1065/CT-1120SI EXT; CT-PET EXT may also apply | Sept. 15, 2026 |
| S Corporation | CT-1065/CT-1120SI | CT-1065/CT-1120SI EXT; CT-PET EXT may also apply | Sept. 15, 2026 |
| C Corporation | CT-1120 / CT-1120CU | CT-1120 EXT | Nov. 16, 2026 |
| Fiduciary / Estate / Trust | CT-1041 | CT-1041 EXT; CT-1127 may extend payment if applicable | Sept. 30, 2026 |
Frequently Asked Questions
Quick answers about Connecticut business tax extensions – but always confirm the current rules with the Connecticut Department of Revenue Services.
Visit Connecticut Department of Revenue ServicesYes. However, the applicable entity-specific requirements listed above must be satisfied. Connecticut grants extensions to LLCs, partnerships, S corporations, C corporations, and fiduciaries, but the rules – including which form to file, how long the extension lasts, and the payment threshold – vary by entity type. For individual returns, see our Connecticut individual tax extension.
Generally no. In other words, pay required tax by the original deadline and confirm the current state payment rules. An extension of time to file does not extend the time to pay – failing to pay by the original deadline can result in penalties and interest, even if the return is filed within the extended window.
No. In practice, partnerships, S corporations, C corporations, and fiduciaries can use different original dates, extension periods, or forms. For 2025 calendar-year returns filed in 2026, partnerships and S corporations generally receive a six-month extension to Sept. 15, 2026; C corporations receive a six-month extension to Nov. 15, observed as Nov. 16, 2026; and fiduciaries receive a five-and-a-half-month extension to Sept. 30, 2026.
Review the Connecticut Department of Revenue Services guidance for the entity’s return. Additionally, the DOR publishes the current CT-1065/CT-1120SI, CT-1120, CT-1041, and related extension forms, along with any changes to extension periods or payment thresholds.
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