CT-1120 CU: Combined Unitary Corporation Business Tax Return (2025)
Connecticut · Connecticut DRS · Used for tax years 2025
Form CT-1120CU is Connecticut’s 2025 Combined Unitary Corporation Business Tax Return. It lists the group’s members and reports combined group tax, credits, payments, and the balance due or overpayment.
What you'll need
Have these forms and details ready, as applicable:
- Member information: Corporation names, taxable status, member numbers, Connecticut tax registration numbers, and federal employer identification numbers (FEINs). Connecticut tax registration numbers must be included for the parent and all taxable members.
- Tax calculations: Form CT-1120CU-NI and Form CT-1120CU-MTB supply the amounts used in Part I.
- Business tax credits: Attach a 2025 Form CT-1120K for each member claiming, using, or sharing a business tax credit.
- Annualized estimated payments: Attach Form CT-1120I if the group annualized its estimated tax payments.
- Payment and credit details: Amounts paid with Form CT-1120 EXT and Forms CT-1120 ESA, ESB, ESC, and ESD; prior-year overpayments; and applicable PE and refundable tax credits.
- Amended returns: Amounts paid with the original return, additional tax paid afterward, and the overpayment shown on the original return or as previously adjusted.
- Direct deposit details: Account type, routing number, account number, and bank name.
Common mistakes
- Using the wrong year's form: The form warns that submitting the correct year's form helps prevent delays in processing the return or refund.
- Completing Part III too soon: Complete Part I, Part II, and Schedule KU before completing Part III.
- Leaving out registration numbers: Include the Connecticut tax registration number for the parent and every taxable member.
- Submitting the member schedule when it is not needed: Page 2 should only be completed and submitted when filing a paper return. List taxable members first.
- Exceeding the credit limit: In Part II, Line 3, do not enter more than the amount on Line 2 in any column.
- Failing to keep a copy: Keep a copy of the return for your records.
Questions people ask
Which filing method is the default?
The form identifies Water’s Edge as the default. Affiliated Group and Worldwide are listed as elections.
Can an overpayment be applied to next year's estimated tax?
Yes. On the 2025 return, Line 9a lets you enter an amount to be credited to 2026 estimated tax. Line 9b is for the amount to be refunded.
Can I request direct deposit of a refund?
Yes. The form says to complete Lines 9c through 9e for a faster refund by direct deposit. It also asks whether the refund will go to a bank account outside the U.S. and asks for the bank name.
What if the group has more than 50 members?
For a paper return, attach replicas of the member schedule page as needed, with the same information, and begin numbering with 51.
Are separate forms needed for certain credit refund requests?
Yes. If any member is exchanging R & D tax credits, file Form CT-1120 XCH separately. If any member is requesting a Student Loan Payment tax credit refund, file Form CT-RSLP separately.