Connecticut made a pivotal change to its pass-through entity tax — once mandatory, it is now elective — and its corporate return is due a month after the federal date. Getting both right is essential for a Connecticut filing calendar.
Connecticut Tax Deadlines at a Glance (2026)
Entity Type | Return Due | Extended Due Date |
|---|---|---|
Individuals (CT-1040) | April 15, 2026 | October 15, 2026 |
C Corporations (CT-1120) | May 15, 2026 | November 15, 2026 |
S Corps / Partnerships (CT-PET) | March 16, 2026 | September 15, 2026 |
Two corrections. The CT-1120 corporate return is due May 15, 2026 — the 15th day of the month following the federal deadline — not April 15, with a six-month extension to roughly November 15. Individuals file by April 15 (extension to October 15), and the pass-through entity return follows the March 16, 2026 deadline.
The PTE Tax Is Now Elective
This is the headline change: Connecticut’s pass-through entity tax, which was mandatory from 2018 through 2023, became elective for tax years beginning on or after January 1, 2024 (PA 23-204). Partnerships and S corporations now make an annual, irrevocable election to pay the 6.99% entity-level tax, with members receiving a credit. Describing Connecticut’s PET as “mandatory” or “required” is no longer correct.
Rates
Connecticut’s individual income tax is graduated across seven brackets from 2.0% up to a 6.99% top rate (the 2024 rate cut lowered the two lowest brackets to 2.0% and 4.5%). The corporate income tax rate is 7.5%, and a 10% surtax on large corporations (generally $100 million or more in gross income) has been extended through the 2028 income year.
Estimates, Extensions, and Penalties
Individual estimated payments (CT-1040ES) are due April 15, June 15, September 15, 2026, and January 15, 2027, required if you expect to owe $1,000 or more. Connecticut charges interest at 1% per month on unpaid tax; an extension covers filing only, not payment.
CPA Action Steps
Describe the PTE tax as elective (annual election), not mandatory
Use May 15 for the CT-1120 corporate return — not April 15
Apply the 6.99% top individual and PTE rates
Factor the 10% large-corporation surtax where applicable
Verify current rates and dates against the Connecticut Department of Revenue Services (portal.ct.gov/drs) before filing.