Connecticut tax deadlines in 2026: filing dates and estimated payments
Deadlines that fall in calendar 2026: the 2025 return and the 2026 estimated payments. Different year? See Connecticut 2025 →
Connecticut deadlines in 2026
| 2025 individual return due | April 15, 2026 |
|---|---|
| Extended filing deadline | October 15, 2026 |
| Payment due | April 15, 2026, extension or not |
| Final 2025 estimated payment | January 15, 2026 |
| 2026 estimated payments | April 15, 2026 · June 15, 2026 · September 15, 2026 · January 15, 2027 |
Conforms to the federal deadline.
Connecticut estimated tax payments in 2026
Your Connecticut income tax after withholding and any PE Tax Credit is $1,000 or more, and you expect withholding (including PE Tax Credit) to be less than your required annual payment; not required if you had no Connecticut tax liability for 2025.
| Q1 (2026 tax year) | April 15, 2026 |
|---|---|
| Q2 (2026 tax year) | June 15, 2026 |
| Q3 (2026 tax year) | September 15, 2026 |
| Q4 (2026 tax year) | January 15, 2027 |
| Voucher | Form CT-1040ES |
| Underpayment safe harbor | Required annual payment is the lesser of 90% of the tax shown on the 2026 Connecticut return or 100% of the tax shown on the 2025 return (if it covered 12 months); farmers and fishermen use 66 2/3% instead of 90%. |
| Pay online | portal.ct.gov |
Underpayment interest is 1% per month until the earlier of April 15, 2027 or payment. Connecticut has no 110% high-income rule. Farmers and fishermen make a single payment due January 15, 2027.
Source: portal.ct.gov, read September 3, 2026. “Estimated payments for the 2026 taxable year are due on or before April 15, June 15, September 15, 2026, and January 15, 2027.”
All 51 jurisdictions in one table: state estimated tax payment dates for 2026.
Connecticut extensions
Every state's rule in one table: which states accept the federal extension in 2026.
| Does Connecticut accept the federal extension? | Only in some cases. See the rule below. |
|---|---|
| State extension form | Form CT-1040 EXT |
| Original due date | April 15, 2026 |
| Extended due date | October 15, 2026 |
| Payment | Still due April 15, 2026. The extension is to file, not to pay. You will be subject to interest and may be subject to a penalty on any tax not paid by the original due date. |
| How to get it | If you expect no additional Connecticut tax and you requested a federal extension, do nothing; otherwise file Form CT-1040 EXT (electronically through myconneCT or on paper) with payment by April 15, 2026. |
Federal extension is honored only when no additional Connecticut tax is due after withholding, estimates and PE tax credit; if tax is due the state form must be filed with payment.
Source: portal.ct.gov, read September 3, 2026. “...and you have requested an extension of time to file your 2025 federal income tax return, you are not required to file Form CT-1040 EXT.”
Federal deadlines in 2026
| 2025 Form 1040 | April 15, 2026 · extension October 15, 2026 |
|---|---|
| 2025 S-corp (1120-S) & partnership (1065) | March 16, 2026 |
| 2025 C-corp (Form 1120) | April 15, 2026 |
| 2026 federal estimated payments (1040-ES) | April 15, 2026 · June 15, 2026 · September 15, 2026 · January 15, 2027 |
Source: IRS Publication 509 and Form 1040-ES instructions, irs.gov.
Frequently asked questions
When are Connecticut state taxes due in 2026?
Your 2025 Connecticut individual income tax return is due April 15, 2026. If that date falls on a weekend or legal holiday, the deadline moves to the next business day. An extension moves the filing deadline to October 15, 2026, but any tax owed is still due on the original date.
When are Connecticut estimated tax payments due in 2026?
Connecticut estimated payments for the 2026 tax year are due April 15, 2026, June 15, 2026, September 15, 2026, January 15, 2027. Use Form CT-1040ES or pay online. The final installment for 2025 was due January 15, 2026.
Does Connecticut accept the federal extension?
Only in some cases. See the rule below. The state form is Form CT-1040 EXT. The extended filing deadline is October 15, 2026, and tax is still due by April 15, 2026.
Does a Connecticut extension give me more time to pay?
No. An extension extends the time to file, not to pay. To avoid penalties and interest, pay what you expect to owe by April 15, 2026.
Dates are the statutory deadlines that fall in 2026 and move to the next business day when they land on a weekend or holiday. Each section links to the source it was checked against. Always confirm with the Connecticut tax agency or the IRS before relying on a date. This is general information, not tax advice.