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Form CT-300, Mandatory First Installment (MFI) of Estimated Tax for Corporations

We have new guidance about Form CT-300. See:
   • New verification requirements for e-file 
   • Frequently asked questions about Form CT-300

E-file options

Benefits include:

  • automatic calculation of amounts due
  • scheduled payments (up to the due date)
  • instant filing confirmation

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E-file mandate


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.

Tax professionals

See Who the tax preparer e-file mandate applies to.

If you don't meet the above conditions

Continue to paper Form CT-300, Mandatory First Installment (MFI) of Estimated Tax for Corporations.