CT-6251: Connecticut Alternative Minimum Tax Return (2025)
Connecticut · Connecticut DRS · Used for tax years 2025
Form CT-6251 calculates Connecticut alternative minimum tax for individuals for 2025. It reports adjustments to federal alternative minimum taxable income, calculates Connecticut minimum tax, and accounts for any credit for alternative minimum tax paid to qualifying jurisdictions
Who files this form
For tax year 2025, you must file Form CT-6251 if either applies:
- You were a Connecticut resident or part-year resident and had a federal alternative minimum tax liability.
- You were a Connecticut nonresident, had a federal alternative minimum tax liability, and had Connecticut-sourced income.
If you meet either condition, you must file even if your Connecticut alternative minimum tax is zero. If you have no federal alternative minimum tax liability, you generally do not need to complete this form.
Special rules apply if you and your spouse file jointly federally but separately in Connecticut. You must recalculate your federal alternative minimum tax liability as if your federal filing status were single. If that calculation produces a federal alternative minimum tax liability, you must calculate Form CT-6251 as a single individual.
What you'll need
Have these forms and details available:
- Your federal Form 6251.
- Your Connecticut Form CT-1040 or Form CT-1040NR/PY, including Schedule 1.
- Your name and Social Security number as shown on your Connecticut return. For a joint return, include your spouse’s name and Social Security number.
- If applicable, federal Form 2555 and the federal Form 6251 Foreign Earned Income Tax Worksheet. The Connecticut Foreign Earned Income Tax Worksheet may also be required; keep it for your records.
- If claiming a Schedule A credit, copies of the alternative minimum tax returns filed with each qualifying jurisdiction. These copies must be attached.
How to file
- Complete Form CT-6251 in blue or black ink.
- Enter the amount from Line 23 on Form CT-1040, Line 9, or Form CT-1040NR/PY, Line 13.
- Attach Form CT-6251 directly behind your Connecticut income tax return. Do not use staples.
- If claiming a Schedule A credit, attach copies of the qualifying jurisdictions’ alternative minimum tax returns directly after Form CT-6251.
- If you need more than two Schedule A columns, create an identical worksheet and attach it to the back of Form CT-6251.
The supplied text does not give a mailing address or e-file instructions.
Common mistakes
- Using the wrong year’s form. The instructions warn that submitting the correct year’s form is necessary to prevent processing delays. Use the 2025 form for tax year 2025.
- Leaving out required credit attachments. Your Schedule A credit will be disallowed if you do not attach a copy of the return filed with the qualifying jurisdiction.
- Using staples or the wrong ink. Do not staple the return, and complete the form only in blue or black ink.
- Overlooking the special exemption instructions for younger filers. If you were under age 24 at the end of 2025, follow the federal Form 6251, Line 5 instructions to calculate your exemption.
Questions people ask
What is Form CT-6251 used for?
It calculates your Connecticut alternative minimum tax liability, which is in addition to regular income tax.
How do part-year residents and nonresidents calculate the tax?
First calculate the Connecticut minimum tax as if you were a Connecticut resident, then apportion it using the Line 18 instructions. Full-year residents enter 1.0000 on Line 18.
Do I need to complete Part 2?
If you completed Part III of federal Form 6251, complete Part 2 of CT-6251. However, if CT-6251 Lines 2 and 4 are both zero, skip Part 2 and enter federal Form 6251, Line 7, on CT-6251, Line 12.
Can I claim credit for alternative minimum tax paid elsewhere?
Connecticut residents and part-year residents may claim a Schedule A credit for qualifying taxes on income taxed by both Connecticut and a qualifying jurisdiction, subject to the credit rules and limits. Qualifying jurisdictions include another U.S. state, a local government within another state, or the District of Columbia. They do not include foreign countries.
Can Connecticut alternative minimum tax paid in a prior year give me a credit?
You may be able to claim a credit against Connecticut income tax. See the instructions to Form CT-8801.