2027 Connecticut Tax Deadlines

Last updated: July 29, 2026

Key Connecticut tax dates at a glance

This block is the single date reference for 2027 Connecticut filing, payment, and extension planning.

• April 15, 2027: First Connecticut estimated tax payment.
• June 15, 2027: Second Connecticut estimated tax payment.
• September 15, 2027: Third Connecticut estimated tax payment.
• January 18, 2028: Fourth Connecticut estimated tax payment.
• March 15, 2028: Connecticut S Corporation and Partnership composite return due.
• April 18, 2028: Connecticut Individual return and payment due.
• May 15, 2028: Connecticut C Corporation return and payment due.
• September 15, 2028: Extended Connecticut S Corporation and Partnership composite returns due, file only.
• October 16, 2028: Extended Connecticut Individual returns due, file only.
• November 15, 2028: Extended Connecticut C Corporation returns due, file only.

When are Connecticut taxes due in 2027?

Connecticut's 2027 calendar-year S Corporation and Partnership composite returns are generally due March 15, 2028; Individual returns are due April 18, 2028, and C Corporation returns are due May 15, 2028. Estimated payments run quarterly during the 2027 year, and extensions move filing only into September, October, or November 2028 by taxpayer type.

When is the Connecticut C Corporation return due?

Connecticut C Corporations file and pay Connecticut corporate income tax by May 15, 2028. The approved 2027 draft uses Form CT-1120 for the calendar-year C Corporation filing.

• Complete Form CT-1120.
• File electronically through myconneCT or approved software where available.
• Pay by the original due date of May 15, 2028.
• Postmark any mailed return by the due date if paper filing is allowed.

What are the Connecticut C Corporation extension rules?

The extended Connecticut C Corporation filing deadline is November 15, 2028. The extension is to file only; payment remains due on May 15, 2028.

When are Connecticut S Corporation and Partnership returns due?

Connecticut S Corporations and Partnerships file their state pass-through returns by March 15, 2028. Payment also remains tied to the original Connecticut due date.

Which Connecticut pass-through forms are required?

• Form CT-1065/CT-1120SI: Connecticut Composite Income Tax Return.
• Schedule CT K-1: Member's Share of Certain Connecticut Items.
• Form CT-1065/CT-1120SI EXT: Extension request when additional time is needed.

What are the Connecticut pass-through extension rules?

The extended Connecticut S Corporation and Partnership filing deadline is September 15, 2028. The extension is to file only; payment remains due on March 15, 2028.

When is the Connecticut Individual income tax return due?

Connecticut Individuals file and pay their Individual income tax returns by April 18, 2028. The approved 2027 draft uses the Connecticut resident and nonresident forms listed below.

Which Connecticut Individual forms are commonly used?

• Form CT-1040: Resident Income Tax Return.
• Form CT-1040NR/PY: Nonresident or Part-Year Resident Income Tax Return.
• Form CT-1040 EXT: Individual extension request when required.

What are the Connecticut Individual extension rules?

The extended Connecticut Individual filing deadline is October 16, 2028. The extension is to file only; payment remains due on April 18, 2028.

When are Connecticut estimated tax payments due?

Connecticut estimated-payment requirements apply under DRS rules after subtracting withholding and credits; electronic payment through myconneCT is encouraged.

• April 15, 2027: First Connecticut estimated tax payment.
• June 15, 2027: Second Connecticut estimated tax payment.
• September 15, 2027: Third Connecticut estimated tax payment.
• January 18, 2028: Fourth Connecticut estimated tax payment.

What Connecticut rules should tax professionals watch in 2027?

Beyond the main filing calendar, Connecticut has form-driven extension and pass-through details that should stay visible in review:

Which Connecticut extension forms matter?

Connecticut extension treatment is form-driven. C Corporations use Form CT-1120 EXT, pass-through entities use Form CT-1065/CT-1120SI EXT, and Individuals use Form CT-1040 EXT when an extension request is required.

What is Connecticut's corporate due-date rule?

For most C Corporations, Connecticut sets the original due date on the 15th day of the fifth month after year-end and the extended due date on the 15th day of the 11th month after year-end.

What pass-through details should teams watch?

Connecticut uses Form CT-1065/CT-1120SI and Schedule CT K-1 for S Corporations and Partnerships, with March 15 and September 15 calendar-year timing in the approved draft.

Tax-professional context: Several key considerations make Connecticut's tax landscape unique for 2027. Connecticut's progressive income tax system provides moderate tax rates, and the state offers various business-friendly provisions. Electronic filing requirements continue to expand, and Connecticut offers specific tax-planning opportunities.

Electronic filing requirements:

• C Corporations and pass-through entities should file electronically through myconneCT.
• Individuals can use Connecticut online filing where available.
• Business deductions can be processed more efficiently through electronic systems.
• Professional preparers must use approved software vendors.

Composite returns for pass-throughs: Connecticut allows composite returns for nonresident partners and shareholders.

R&D credit carryforward: Research and development credits can be carried forward for multiple years.

Progressive tax rates ranging from 2% to 6.99%: Connecticut provides competitive progressive tax rates for Individuals.

Property tax credit for qualifying residents: Connecticut offers property tax credits for eligible taxpayers.

Pass-through entity taxation:

• Composite return elections may apply for nonresident owners.
• Entity-level tax elections are available.
• Withholding requirements can apply for nonresident partners and shareholders.
• Credit mechanisms may apply for entity-level taxes paid.

Business incentives and credits:

• Manufacturing assistance programs.
• Research and development credits.
• Job creation incentives.
• Urban and industrial site reinvestment credits.

Retirement income considerations:

• Military retirement pay exemptions may apply.
• Social Security benefits treatment considerations.
• Pension income considerations for residents.

Which sources were used for this Connecticut deadline guide?

The sources below are placed above the CTA so Webflow editors and reviewers can verify the deadline logic before publishing.

• Connecticut DRS Corporation Business Tax Information.
• Connecticut DRS Composite Income Tax Information.
• Connecticut DRS Individual Income Tax Information.
• Connecticut DRS Corporation Forms.

Connecticut tax deadlines for surcharge and PTET

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