The due date for calendar year taxpayers is May 15. The due date for fiscal year taxpayers is the fifteenth day of the fifth month after the close of the taxable year. Interest of 12% per year, calculated daily, accrues on any tax liability that you have not paid by the original due date of your tax return.

A corporation is allowed an automatic extension to file its tax return of up to six months following the prescribed filing date. You are not required to apply for this extension. The tax, penalty, and interest must be paid when the return is filed.

The department may grant an additional extension of time for the filing of a return whenever in its judgment good cause exists.

How Should a Corporation File?
If you file electronically, you do not need to mail the CLT-4 to us unless we ask for a copy. When you file electronically, you represent that you have retained the required documents in your tax records and will provide them upon the department’s request. Montana law requires that your return be signed by the corporation’s president, vice president, treasurer, assistant treasurer or chief accounting officer, but the authorized officer may sign electronically. The act of submitting an electronic return constitutes the officer’s signature and a declaration that they are the officer identified in the return as signing the return.

For additional information, please visit the State of Montana Department of Revenue website.

If you choose not to file electronically, please mail your tax returns to:
Montana Department of Revenue
PO Box 8021
Helena, MT 59604-8021