Connecticut Business Tax Requirements
Understand your Connecticut business tax obligations and file your state forms accurately with TaxZerone. Learn which taxes apply to your business type, how to stay compliant, and what forms you need to file with the Connecticut Department of Revenue Services (DRS).
What are the Business Tax Forms in Connecticut?
Connecticut requires every business operating within the state to comply with state tax laws and
file specific tax forms based on its structure—whether you’re a sole proprietor, partnership, corporation, or LLC.
Here’s a breakdown of the most common filing requirements for each business type:
Sole Proprietorship &
Single-Member LLC
- Form CT-1040 – Connecticut Resident Income Tax Return
- Form CT-1040NR/PY – Nonresident or Part-Year Resident Return
- Schedule C (Federal Form 1040) - Profit or Loss from Business (attached to federal return)
Partnership & Multi-Member LLC
- Form CT K-1 – Partner’s or Shareholder’s Share of Income, Deductions, and Credits
- Form REG-1 – Business Tax Registration for Sales, Use, and Withholding Taxes
C Corporation
- Form CT-1120 –Corporation Business Tax Return
- Form CT-1120CU – Combined Unitary Corporation Business Tax Return (if applicable)
S Corporation
- Form CT-1065/CT-1120SI – S Corporation Business Tax Return
- Form CT K-1 – Shareholder’s Share of Income, Deductions, and Credits
Pass-Through Entities
- Form CT-1065/CT-1120SI – Composite Income Tax Return
- Form CT-1041 – Fiduciary Income Tax Return (if applicable)
Tax-Exempt Organizations
- Form CT-990T – Connecticut Corporation Business Tax Return for Exempt Organizations (if they have unrelated business income)
Additional California Business Tax Forms
- Form CT-941 – Withholding Tax Return for Employers
- Form CT-945 – Annual Withholding Return for Nonpayroll Amounts
- Form OS-114 – Sales and Use Tax Return
- Form OP-424 – Business Entity Tax Return (for prior years before repeal in 2020)
What are the deadlines for the Business Tax Forms in Connecticut?
Understand the key deadlines for filing Connecticut business taxes for all entity types:
| General Partnerships | Return due date: 15th day of 3rd month |
| Payment due date: 15th day of 3rd month | |
| Limited Partnerships / LLPs / LLLPs | Return due date: 15th day of 3rd month |
| Payment due date: 15th day of 3rd month | |
| Limited Liability Companies (LLCs) | Return due date: 15th day of 3rd month |
| S Corporations | Return due date: 15th day of 3rd month |
| Payment due date: 15th day of 3rd month | |
| C Corporations | Return due date: 15th day of the month |
| Payment due date: 15th day of the month | |
| Tax Exempt Organizations | Return due date: 15th day of 5th month |
| Payment due date: 15th day of 5th month | |
| Pass-Through Entities | Return due date: 15th day of 3rd month |
| Payment due date: 15th day of 3rd month | |
| Sales and Use Tax | Return due date:
|
| Withholding Tax | Return due date:
|
What Business Extension Forms are required in Connecticut?
Business Type
- Corporations & Unitary Combined Groups Form CT-1120 EXT
- Partnerships & S Corporations Form CT-1065/CT-1120SI EXT
- Trusts & Estates Form CT-1041 EXT
- All Business Types (if payment time extension needed)
Form CT-1127
Online Payment Option
Connecticut business tax payments can also be made online through the DRS Taxpayer Service Center (TSC).
What are the Extended due date for Business Tax
Forms in Connecticut?
Understand the key extended deadlines for filing Connecticut business taxes for all entity types:
General Partnerships
Extended due date:
6-month
of extension
Limited Partnerships / LLPs / LLLPs
Extended due date:
6-month
of extension
Limited Liability Companies (LLCs)
Extended due date:
6-month
of extension
S Corporations
Extended due date:
6-month
of extension
C Corporations
Extended due date:
6-month
of extension
Tax-Exempt Organizations
Extended due date:
6-month
of extension
Pass-Through Entities
Extended due date:
6-month
of extension
Sales and Use Tax
Extended due date:
No extension for filing. Returns must be filed by the
regular due dates
Withholding Tax
Extended due date:
No filing extension; returns must be filed by standard deadlines
Connecticut Business Tax Extension Filing Requirements
To qualify for a business tax extension in Connecticut, your business must:
- File by the original due date to avoid penalties and interest—extensions apply only to filing, not payments.
- Submit the correct Connecticut extension form based on ybased on your entity type:
- Form CT-1120 EXT for corporations
- Form CT-1065/CT-1120SI EXT for partnerships and S-corporations
- Form CT-1041 EXT for trusts and estates
- Estimate and pay any taxes owed by the original return due date, even if you file for an extension.
- Attach a copy of your federal extension (Form 7004) if applicable—Connecticut generally honors a valid federal extension.
- Meet the 6-month extension window, which typically extends your filing deadline but not your payment deadline.
- Keep proof of filing and payment confirmations from the Connecticut Department of Revenue Services (DRS) for compliance.
Connecticut Business Tax Rates
Business tax rates vary depending on your entity type:
C Corporation
7.5%
of net income (Plus a 10% surtax applies to corporations with gross income of $100 million or more or those filing as part of a combined unitary group.)
S Corporation
6.99%
of Connecticut-source income (Pass-Through Entity Tax rate)
LLCs
6.99%
of Connecticut-source income (if subject to Pass-Through Entity Tax).
Partnerships (LP & LLPs)
6.99%
of Connecticut-source income (Pass-Through Entity Tax rate applies if elected or required)
Exempt Organizations
Exempt
Generally, exempt but may be taxed on unrelated business income
Estimated Tax Payments for Connecticut Businesses
Businesses in Connecticut must make estimated tax payments if they expect to owe $1,000 or more in
state income tax for the year. These prepayments help you avoid underpayment penalties and interest.
Payment Deadlines
1st payment
March 15
27% of current year tax OR 30% of last year’s tax
2nd payment
June 15
63% of current year tax OR 70% of last year’s tax
3rd Payment
Sept 15
72% of current year tax OR 80% of last year’s tax
4th Payment
Dec 15
90% of current year tax OR 100% of last year’s tax
Who should pay
Corporation & Unitary Combined Groups
- Required to make estimated payments if expected tax liability exceeds $1,000.
- Use Form CT-1120 ESA for estimated corporation business tax payments.
Pass-Through Entities (Partnerships, S Corporations, LLCs)
If subject to the Pass-Through Entity Tax (6.99%), make estimated payments using Form CT-1065/CT-1120SI ESA.
Trusts & Estates
Trusts & Estates Use Form CT-1041 ES for estimated fiduciary income tax payments.
Missed Payments: Late or missed estimated payments may result in interest and penalties under Connecticut law.
Penalties and Interest for Business in Connecticut
In Connecticut, interest and penalties apply to any portion of tax not paid by the original due date,
even if an extension to file has been granted.
Penalty for late payment or Late filing
- The penalty for late payment or underpayment of tax is 10% of the unpaid tax not paid by the original due date.
- A business can avoid this penalty if it:
- Files Form CT-1127 (Application for Extension of Time to Pay),
- Is granted an extension of time to pay, and
- Pays the full amount due by the end of the approved extension period.
- If no tax is due, a $50 minimum penalty may apply for filing late.
Electronic Payment Penalties
If your business is required to make electronic payments and fails to do so, the following graduated penalties apply:
- First offense: 10% of the payment amount (up to $2,500)
- Second offense: 10% of the payment amount (up to $10,000)
- Third and subsequent offenses: 10% penalty, no maximum limit
Penalty for Failure to file
- If the Department of Revenue Services (DRS) files a return on behalf of your business, the penalty is 10% of the balance due or $50, whichever is greater.
- If a business is required to file an amended return(Form CT-PET) and fails to do so, an additional penalty may apply.
Penalty for Willful Failure to File or Pay
If a business willfully fails to file a return or pay the tax due, it may face:
- A fine up to $1,000, or
- Imprisonment up to one year, or both.
Penalty for Willful Filing of a Fraudulent or False Return
If a business willfully files a fraudulent or materially false return, it may be subject to:
- A fine up to $5,000, or
- Imprisonment up to five years, or both.
Interest
If the business does not pay the tax when due, interest is charged at 1% per month or a fraction of a month until the tax is fully paid.
- Interest on late or underpaid tax cannot be waived under any circumstance.
How TaxZerone can Help You?
TaxZerone supports federal tax filing and also guides you through Connecticut-state requirements to help your business stay compliant. While Connecticut business taxes must be filed directly with the Department of Revenue Services (DRS),TaxZerone provides the guidance you need to:
- Understand which Connecticut business tax forms apply to your entity type
- Know your state deadlines and payment requirements
- Prepare for extensions and estimated tax payments
- Avoid penalties by staying informed and organized
With TaxZerone, you can manage your federal filings easily while ensuring your Connecticut state obligations are met on time and correctly.
File Smarter, Not Harder!
Simplify your Connecticut and federal business tax filings with TaxZerone.
Stay compliant, avoid penalties, and file confidently
Frequently Asked Questions
1. What forms do different business types need to file in Connecticut?
In Connecticut, the forms a business needs to file depend on its type. Sole proprietors file Form CT-1040, while partnerships, multi-member LLCs, and S corporations file Form CT-1065/CT-1120SI and provide Schedule CT K-1 to their members or shareholders. C corporations use Form CT-1120, or Form CT-1120CU if part of a combined unitary group. Tax-exempt organizations with unrelated business income must file Form CT-990T.
Additionally, employers are required to file sales and use tax returns and withholding tax returns separately from their business income filings.
2. How do I make a payment for Connecticut business taxes?
- Pay by ACH Debit/Direct Payment: Using this option authorizes DRS to electronically withdraw a payment from your bank account (checking or savings) on a date you select, up to the due date.
- Pay by Credit Card or Debit Card: You may elect to pay your tax liability using a credit card (American Express®, Discover®, MasterCard®, Visa®) or a comparable debit card.
- A convenience fee will be charged by the credit card service provider.
- You will be informed of the fee amount and may choose to cancel the transaction.
- Your payment will be effective on the date the charge is made.
3. Who should file Form CT-1065/CT-1120SI?
4. Does filing a federal extension automatically extend my Connecticut business return?
Yes. Connecticut generally honors a valid federal extension (Form 7004). However, you must file the corresponding Connecticut extension form—such as Form CT-1120 EXT, CT-1065/CT-1120SI EXT, or CT-1041 EXT—and pay any taxes owed by the original due date to avoid penalties and interest.
