Required for All

Form REG-1: Business Tax Registration
Use Form REG-1 to obtain a Connecticut tax registration number or to register for additional tax types under your current Connecticut tax registration number.

Form W2: Wage and Tax Statement
All businesses that will pay wages to employees will need to complete this form for each employee and file it with the IRS. 

Form W3: Transmittal of Wage and Tax Statement
If you needed to fill out the W2 form, you will also need to complete the W3 and file it with the IRS. 

Instructions for W2 and W3 Tax Forms
In order to ensure you've filled out these forms correctly, we've linked the instructions provided by the IRS. 

Form CT-W3: Connecticut Annual Reconciliation of Withholding
After the end of the year, you must file an annual reconciliation with the Department of Revenue Services (DRS) that summarizes the employee taxes you’ve withheld during the year. Use this form to report this information.

Form CT-W4: Employee’s Withholding Certificate
This form provides your employer with the necessary information to withhold the correct amount of Connecticut income tax from your wages to ensure that you will not
beunderwithheld or overwithheld. A new Form CT-W4 should be completed at least once a year or if your tax situation changes.

Form OP-424: Business Entity Tax Return
The Business Entity Tax (BET) is a $250 tax due every other taxable year and is imposed on all S corporations, limited liability companies (LLCs), limited liability partnerships (LLPs), and limited partnerships (LPs). The BET applies to businesses formed under Connecticut law or those that transact business within Connecticut.

Connecticut Income Tax Changes Affecting Pass-Through Entities
This Informational Publication addresses frequently-asked question about changes made to the income tax affecting pass-through entities during the 2006 session of the Connecticut General Assembly.

A Guide to Estimated Connecticut Income Taxes                    
Explains the requirements for paying estimated Connecticut income tax. Note that you can be charged interest for underpayment this estimated amount even if you pay all the full sum of what you owe by the April 15 filing deadline.

A Guide to Calculating Your Annualized Estimated Income Tax Installments and Worksheet CT-1040 AES
If you use the annualized estimated income tax installment method, your required installment for one or more periods may be less than the amount of the installment calculated using the regular installment method.

Form CT-NAICS: NAICS Codes for Principal Business Activity for Connecticut Tax Purposes
FORM CT-NAICS NAICS Codes for Principal Business Activity for Connecticut Tax Purposes. You must select the code that best matches your primary business activity.