Enterprise
Individual & Small Business
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Federal 2026 estimated tax due dates, for comparison: April 15, 2026, June 15, 2026, September 15, 2026, January 15, 2027.
Who must pay Connecticut estimated tax?
You must make estimated income tax payments if: 1. Your Connecticut income tax, after taking into account your Connecticut tax withheld, and any Pass-Through Entity Tax Credit (PE Tax Credit) you are allowed to claim, is $1,000 or more; and 2. You expect your Connecticut income tax withheld (including any PE Tax Credit) to be less than your required annual payment for the 2026 taxable year.
How do you avoid a Connecticut underpayment penalty?
Required annual payment is the lesser of 90% of the 2026 Connecticut income tax (66 2/3% farmers/fishermen) or 100% of the 2025 Connecticut income tax (if a 12-month 2025 return was filed). Nonresidents/part-year residents with no Connecticut-sourced income in 2025 must use 90% of 2026 tax. No 110% rule. Filing the 2026 return on or before January 31, 2027 and paying in full avoids interest for the January 15, 2027 installment.
How much should you pay?
Start with your federal estimate: the free Quarterly Estimated Tax Calculator works out your 2026 federal payments and safe harbor. Connecticut figures its own tax, so the state amount is separate.