CT-1040X: Amended Income Tax Return for Individuals (2024)
Connecticut · Connecticut DRS · Used for tax years 2024
Form CT-1040X is the 2024 Amended Connecticut Income Tax Return for Individuals. It reports changes to a previously filed return, including income, taxes, credits and payments, and calculates any refund or additional amount owed.
Who files this form
Use the 2024 Form CT-1040X to amend a previously filed 2024 Connecticut individual income tax return.
You must file if any of these situations causes your Connecticut income tax to be overpaid or underpaid:
- The IRS or a federal court changes or corrects your federal return.
- You file a timely amended federal return.
- You claimed a credit for taxes paid to a qualifying jurisdiction, and that jurisdiction's tax officials or courts change your return in a way that changes your allowable credit.
- You claimed that credit and file a timely amended return with the qualifying jurisdiction that changes your allowable credit.
- You discover a mistake or omission on your Connecticut return.
Do not use this version for another tax year or to amend Form CT-1041 or Form CT-1065/CT-1120SI.
When it's due
For amendments to tax year 2024 returns, the text gives these filing periods:
- Federal or qualifying-jurisdiction changes: For the audit, court correction, or timely amended-return situations described in the form, file no later than 90 days after the final determination date. Filing within that period allows the resulting overpayment to be refunded or credited even if the usual Connecticut refund time limit has expired.
- Other mistakes or omissions: File no later than three years after the return's due date. If you timely requested a filing extension, the deadline is three years after the date you filed or three years after the extended due date, whichever is earlier.
The text also provides an extension of the refund or credit time limit for qualifying financial disability.
What you'll need
Have your original or previously adjusted 2024 Connecticut return available. Attach supporting forms and schedules for the items you change, and write your name and SSN(s) on all attachments.
Depending on your changes, you may also need:
- Federal or other-state changes: Applicable IRS audit or other-state results, federal Form 1040X or Form 1045, the other state's amended return, supporting documents, and proof of the final determination.
- Nonresident or part-year resident income: A corrected Schedule CT-SI. Part-year residents must also attach a corrected Schedule CT-1040AW.
- Credit for taxes paid to a qualifying jurisdiction: A copy of the return filed with that jurisdiction.
- Alternative minimum tax or allowable credit changes: Corrected Form CT-6251, Schedule CT-IT Credit, or Form CT-8801, as applicable. Write “Amended” across the top.
- Credits claimed: Schedule 3 for the property tax credit, Schedule CT-EITC, Form CT-1040 CRC, Schedule CT-PE, or the Historic Home Rehabilitation tax credit voucher, as applicable.
Use Forms W-2, 1099, and Schedules CT K-1 showing Connecticut withholding to complete the Withholding Schedule, but do not send those documents. If you have more than five, complete Supplemental Schedule CT-1040WH and attach it to the back of the return.
How to file
File online: File and pay electronically through myconneCT.
Complete the return:
- Identify each change using your original return. Line numbers may differ on CT-1040X.
- Complete Schedules 1 through 4 with corrected amounts, or the original amounts where nothing changed.
- Enter original or previously adjusted amounts in Column A, net increases or decreases in Column B, and correct amounts in Column C. If an amount did not change, copy Column A into Column C.
- Explain each change on Page 3, including the line number, and attach supporting forms and schedules.
- For applicable federal or state changes, check the box on Page 1 and enter the final determination date.
- Sign the declaration on Page 1. Your spouse must also sign a joint return. Keep a copy for your records.
File by mail: Send the return to:
Department of Revenue Services
PO Box 2935
Hartford CT 06104-2935
Make your check payable to Commissioner of Revenue Services. Write “2024 Form CT-1040X” on the check. Adding your SSN(s) to the check is optional. Do not use staples.
Common mistakes
- Using the wrong year's form: Each form is year-specific. The wrong version can delay processing.
- Trying to change an original election: CT-1040X cannot change an overpayment from next year's estimated tax to a refund, or change contributions to designated charities.
- Leaving withholding columns incomplete: Complete every column of the Withholding Schedule or the withholding will be disallowed. Do not send Forms W-2, 1099, or Schedules CT K-1.
- Missing required credit attachments: The property tax credit requires Schedule 3, the earned income tax credit requires Schedule CT-EITC, and the credit for taxes paid to qualifying jurisdictions requires copies of those returns. Missing attachments will cause those credits to be disallowed.
- Including penalty and interest on Line 23: This line is for tax paid with the original return and additional tax paid afterward, not penalty or interest.
- Subtracting out-of-state income on Line 49: The form specifically says not to include it there.
- Forgetting the signature: Taxpayers must sign the declaration on Page 1.
Questions people ask
Can I use this form to amend a different tax year?
No. This version is only for a previously filed 2024 Connecticut individual income tax return. Use the correct year's form.
What if an amount has not changed?
Enter the amount from Column A in Column C. For Schedules 1 through 4, enter the original amounts where you are not making corrections.
Will I owe interest on additional tax?
Interest accrues at 1% per month or fraction of a month from the original due date until the tax is paid in full. A fraction of a month counts as a whole month.
Can part-year residents claim the Connecticut earned income tax credit?
No. Only full-year residents can claim it. Part-year residents and nonresidents do not qualify.
Can I amend an earlier return to claim a credit for income I repaid later?
Do not use CT-1040X for that purpose. The text directs you to file Form CT-1040 CRC, Claim of Right Credit, with your Connecticut income tax return for the later taxable year.