CT-2210: Underpayment of Estimated Income Tax by Individuals, Trusts, and Estates (2025)

Who files this form

Form CT-2210 is for individuals, trusts, and estates filing Form CT-1040, CT-1040NR/PY, or CT-1041 who underpaid Connecticut estimated income tax.

File it with your 2025 Connecticut return if a reason in Part 1 applies. These reasons include:

• Using the annualized income installment method because your income varied during the year.
• Basing payments on your 2024 tax when you filed jointly for either 2024 or 2025, but not both.
• Applying withholding on the dates it was actually withheld instead of in equal installments.
• Qualifying as a farmer or fisherman.
• Being unable to use prior-year tax because you were a 2024 part-year resident or nonresident with no Connecticut-sourced income and were not required to file.
• Having no 2024 Connecticut tax liability and not filing a 2024 return, while either a full-year resident or a part-year resident or nonresident with Connecticut-sourced income. Check Box F or G, as applicable, and attach Page 1 only.

You may also file to calculate and pay interest with your return. Otherwise, DRS will calculate any underpayment interest and send a bill.

Part 2 tells you not to complete or file the form if Line 4 is less than $1,000 or Line 7 is zero or less.

When it's due

For tax year 2025, the printed estimated-payment dates are April 15, 2025; June 15, 2025; September 15, 2025; and January 15, 2026. If a due date falls on a Saturday, Sunday, or legal holiday, payment is timely on the next business day. Fiscal-year filers should follow federal filing dates.

Special timing rules for 2025:

• January 31, 2026: File your 2025 return and pay the full amount payable by this date to avoid the January 15, 2026 estimate and underpayment interest for the fourth installment. Do not complete Schedule B, Worksheet D, if you meet this rule.
• Farmers and fishermen: Pay the one required installment by January 15, 2026, or file your 2025 return and pay the full amount payable by March 1, 2026.
• April 15, 2026: Underpayment interest stops accruing on this date or the date the underpayment is paid, whichever is earlier.

File CT-2210 with your Connecticut income tax return.

What you'll need

Have the following information available, as applicable:

• Your 2025 Connecticut return and your 2024 Connecticut return if using prior-year tax.
• Your name and Social Security number as shown on your return, plus your spouse’s information for a joint return. Trusts and estates use the entity name, fiduciary’s name, and federal employer identification number.
• Forms W-2 or 1099 and Schedule CT K-1 showing Connecticut withholding.
• Schedule CT-PE, Line 1, for your Pass-Through Entity Tax Credit.
• Amounts and dates of estimated payments and late payments. If using actual withholding dates, have the cumulative withholding amounts for each period.

If using the annualized income installment method, attach Schedule A and your calculations of Connecticut adjusted gross income for each period. Nonresident and part-year resident individuals must also include Worksheet 1. Use the applicable CT-1040NR/PY or CT-1041 schedules and worksheets to determine Connecticut-sourced income.

How to file

• Electronic filing: Select the CT-2210 indicator on your Connecticut income tax return. Complete CT-2210 and upload it as an attachment.
• Paper filing: Check the CT-2210 box on the front of your Connecticut income tax return and place the form at the back of the completed return. The supplied text does not give a mailing address.

Follow any Part 1 instruction to stop and attach Page 1 only. Otherwise, complete Part 2 and the applicable Part 3 calculations. Use Schedule B for periods showing an underpayment, and enter the total interest from Part 3, Line 17, on the appropriate line of your Connecticut return.

Attach Schedule A and supporting calculations if using annualized income. Keep copies of the worksheets and schedules for your records.

Common mistakes

• Using the wrong year’s form. The instructions warn that submitting the correct year’s form prevents processing delays.
• Forgetting the return indicator or attachment. Select or check the CT-2210 indicator and attach the required form pages.
• Reducing Part 2, Line 1, by payments or credits. Do not subtract estimated payments, withholding, or PE Tax Credits on that line.
• Including the wrong amounts as Connecticut withholding. Do not include estimated payments or taxes withheld for the IRS or other jurisdictions.
• Using annualized income for only some installments. If you use this method for one installment, you must use it for all installments and attach the required calculations.
• Using the individual Schedule A periods for a trust or estate. Trusts and estates must use the separate period-ending dates and annualization amounts stated in the instructions.
• Assuming a refund means no interest is due. Interest is calculated separately for each installment, so a refund or a later catch-up payment does not necessarily eliminate earlier underpayment interest.

Questions people ask

How is my required annual payment calculated?

Generally, it is the smaller of 90% of your 2025 Connecticut income tax or 100% of your 2024 Connecticut income tax if your filed 2024 return covered 12 months. Special rules apply to farmers, fishermen, filing-status changes, and some taxpayers who cannot use prior-year tax.

What is the underpayment interest rate?

Interest is 1% per month or fraction of a month. Any fraction of a month counts as a whole month.

Can uneven income reduce my interest?

Yes. The annualized income installment method may reduce or eliminate one or more required installments if your income varied during the year. Check Box A and complete Schedule A and the required supporting calculations.

What if I had no Connecticut tax liability in 2024?

If you did not file a 2024 return because you had no Connecticut tax liability, you may qualify for Box F or G. Box F applies to full-year Connecticut residents. Box G applies to part-year residents or nonresidents who had Connecticut-sourced income. Check the applicable box, stop, and attach Page 1 to your return.

Does DRS calculate interest if I do not file CT-2210?

Yes. If you do not file the form, DRS will calculate any estimated-tax underpayment interest and send a bill. You must still file CT-2210 when a Part 1 reason applies.

Official sources

• https://portal.ct.gov/-/media/drs/forms/2025/income/ct-2210_1225.pdf