Montana Filing Due Date: Corporation tax returns are due by May 15 — or by the 15th day of the 5th month following the end of the taxable year (for fiscal year filers).
Extended Deadline with Montana Tax Extension: Montana offers a 6-month extension, which moves the corporation filing deadline to November 15 (for calendar year filers).
Montana Tax Extension Form: Montana’s business extension is automatic, so there’s no formal application or written request to submit.
Montana Extension Payment Requirement: An extension of time to file is not an extension of time to pay. If you owe Montana tax, it must be paid by the original due date to avoid penalties and interest. You can make a Montana extension payment with Form CT, or pay electronically through Montana’s Online Services portal: revenue.mt.gov/online_services