An extension to file is not an extension to pay tax.
Connecticut's extension is automatic in one narrow case - a taxpayer who requested a federal extension and expects to owe no additional Connecticut tax does not need to file anything separately. Everyone else, including any taxpayer who owes additional Connecticut tax, must file Form CT-1040 EXT and pay the tentative tax due by the original due date.
| Item | Detail |
|---|---|
| Form required | Form CT-1040 EXT, unless a federal extension was requested and no additional Connecticut tax is owed |
| Extension length | 6 months, matching the federal extension period, to October 15, 2026 |
| Payment rule | The tentative Connecticut tax shown on the form must be paid by the original due date; a 10% penalty applies if the tax shown on the completed return exceeds the tentative payment (subject to limited exceptions), plus interest on any underpayment |
| Authority | Conn. Agencies Regs. §12-723-1 (extension of time for filing returns) |