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Official form guide
Form CT1: CT-1
Form CT‑1 is the Connecticut Corporate Income Tax Return. It is filed by corporations that have Connecticut taxable income or are otherwise required to pay the state’s corporate tax.
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IRS Form CT1 - CT-1
Form CT‑1 is the Connecticut Corporate Income Tax Return. It is filed by corporations that have Connecticut taxable income or are otherwise required to pay the state’s corporate tax.
Risk Radar
Scan points- 1A single mis‑calculated credit can add thousands of dollars in penalties.
- 2Mis‑classifying non‑Connecticut income as taxable
- 3Omitting required Schedule CT‑1A credits
- 4Using the wrong tax year version of the form
- 5Incorrectly calculating apportionment for multistate corporations
Plain English
If your business is a corporation and earns money that is taxed by Connecticut, you use this form to tell the state how much you earned and how much tax you owe. The form calculates the tax based on your Connecticut‑source income and allowable deductions.
Submission Date
- Filing date: 2026-01-14 17:26:06
- Preparation window: collect IDs, supporting records, and signatures in advance.
- Final review: verify names, dates, and required fields before submission.
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What this form is for
- Use this form when your corporation has Connecticut taxable income.
- Do not use if you are a non‑corporate entity (partnership, sole proprietorship).
- Check Form CT‑1‑ES for estimated tax payments.
Form selector
Use this form or another form?
No Connecticut taxable income
Zero‑tax return
✓ Verify zero‑tax eligibility before filing
Corporation filing a short‑form return
Simplified schedule for small corporations
✓ Confirm eligibility thresholds
Amended return needed
Corrects previously filed CT‑1
✓ Attach original return and explain changes
Deadline or filing window
For calendar‑year corporations, the filing deadline is April 15. If the 15th falls on a weekend or holiday, the deadline moves to the next business day. Extensions can be requested using Form CT‑1‑EXT, which extends the filing date but not the payment deadline.
- —Connecticut taxable income | Federal taxable income +/- CT adjustments | CT taxable income | Verify all adjustments are supported
Checklist
What you need before filling it out
Federal taxable income
Form 1120/1120‑S line 30 · Federal return
Connecticut adjustments
Schedule CT‑1A worksheet · Internal accounting records
Tax credits claimed
Schedule CT‑1A credit lines · Credit documentation (e.g., R&D credit)
Payments made
Cancelled check or electronic confirmation · Bank records
Before you submit
- 1Confirm you are using the 2024 edition of Form CT‑1.
- 2Match federal taxable income to the amount on your Form 1120/1120‑S.
- 3Complete all Connecticut adjustment worksheets.
- 4Calculate tax, credits, and net tax due correctly.
- 5Attach Schedule CT‑1A for any credits claimed.
- 6Include any required payments or proof of payment.
- 7Sign and date the return as an authorized officer.
- 8If filing paper, use the correct mailing address and postage.
- 9If filing electronically, verify successful upload receipt.
- 10Retain a copy of the filed return and all supporting documents.
How to file this form
- 1Log in to CT‑FILE or download the printable PDF.
- 2Enter corporation identification information (EIN, address, tax year).
- 3Input federal taxable income and apply CT adjustments.
- 4Enter calculated tax, credits, and any payments.
- 5Review all totals for arithmetic errors.
- 6Attach required schedules and supporting documents.
- 7Submit electronically or mail the complete packet.
Known limitations
- 1The form does not calculate multistate apportionment automatically; manual calculations are required.
- 2Electronic filing may reject the return if the PDF version is not the current edition.
- 3The instructions provide examples but not exhaustive lists of all possible credits.
- 4Late‑filing penalties are not shown on the form; separate calculation may be needed.
Field map
Compact field-by-field guide
Employer Info
1 items
Full legal name and Employer Identification Number.
Quarter
1 items
Select the calendar quarter this return covers.
Wages
1 items
Sum of all wages, tips, and other compensation paid to employees during the quarter.
Withholding
1 items
Total federal income tax withheld from employee paychecks.
SS & Medicare
1 items
Wages subject to Social Security tax (capped) and Medicare tax (uncapped).
Deposit
1 items
Indicate your deposit schedule: monthly, semiweekly, or next-day rule if over $100k.
Signatures
1 items
Must be signed by an authorized officer or agent of the employer.
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Fillable formOpen in Editor->The latest edition of Form CT‑1 is the 2024 version, released October 2023. Verify the edition date before filing.
What changed or needs a fresh check
- Edition date: Verify the form shows 2024 edition (released Oct 2023).
- Fee: No filing fee for the return itself, but payments may be required.
- Mailing address: Use the address in the 2024 instructions for paper filings.
- Electronic filing: Ensure you have a CT‑FILE account and the correct e‑file version.
- Signature block: Include an authorized corporate officer’s signature and title.
Quick Facts
Downloads
After you file
- 1Save the electronic filing confirmation or certified mail receipt.
- 2Store a copy of the signed return and all attachments for at least seven years.
- 3Monitor your account on the Connecticut DRS portal for payment processing or refund status.
- 4If you receive a notice, compare the amounts to your original filing to identify discrepancies.
- 5Adjust future estimated payments based on the actual tax liability reported.
- 6Update your corporate records with the filing date and any tax due.
Sources
- SRCForm CT‑1 title and purposefound in Connecticut DRS official form description.
- SRCFiling deadline (15th day of fourth month)stated in CT‑1 instructions.
- SRCElectronic filing via CT‑FILEmentioned in DRS filing guidance.
- SRCEdition date (2024)listed on the form cover page.
- SRCSignature requirementindicated in the form’s certification block.
- SRCSchedule CT‑1A credit worksheetreferenced in the instructions.
- SRCExtension form CT‑1‑EXTnoted as the amendment for filing extensions.
- SRCNot clearly stated in the provided official source
Common confusion points
Connecticut taxable income vs. Federal taxable income
Adjustments are easy to miss
→ Re‑run the CT adjustment worksheet
Credit eligibility
Credits have specific documentation rules
→ Verify each credit’s supporting schedule
Apportionment method
Different methods for service vs. sales
→ Use the method prescribed for your industry
Electronic vs. paper filing deadline
Some extensions apply only to e‑filing
→ Check the extension form instructions
Signature requirement
Corporate officer vs. authorized agent
→ Ensure the signer has proper authority
Workflow map
Related forms and next steps
Before
Current
After
Often used with
⚠ If something goes wrong
- Form CT‑1‑E (Request for penalty abatement)
Source transparency
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