Form CT-300, Mandatory First Installment (MFI) of Estimated Tax for Corporations
We have new guidance about Form CT-300. See:
- Web File Form CT-300 directly from your Business Online Services account—it’s FREE.
- E-file Form CT-300. See Approved software developers for corporation tax e-file.
- automatic calculation of amounts due
- scheduled payments (up to the due date)
- instant filing confirmation
You must have an Online Services account to access certain services.
If you are viewing this page on your computer, then you're probably required to e-file Form CT-300. You must electronically file Form CT-300 if you:
- do not use a tax professional to file;
- use a computer to prepare, document, or calculate your tax forms; and
- have broadband Internet access.
If you file by paper and meet the above conditions, you are subject to penalties.
Most corporation taxpayers are required to e-file Form CT-300, Mandatory First Installment (MFI) of Estimated Tax for Corporations
You can file Form CT-300 online by using our Web File Online Services, or through approved software for corporation tax e-file.
For more guidance, see Form CT-300-I, Instructions for Form CT-300. To learn how to avoid common corporation tax filing errors, see Get your refund on time and avoid penalties and interest.