Mont. Code Ann. § 15-36-321 — Statute Of Limitations

15-36-321 . Statute of limitations. (1) Except as otherwise provided in this section, a deficiency may not be assessed with respect to the year for which a return is filed unless the notice of additional tax proposed to be assessed is mailed within 5 years from the date on which the return was filed. For the purposes of this section, a return filed before the last day prescribed for filing is considered as filed on the last day. If the taxpayer, before the expiration of the period prescribed for assessment of the tax, consents in writing to an assessment after that time, the tax may be assessed at any time prior to the expiration of the period agreed upon.
(2) A refund or credit may not be allowed or paid with respect to the year for which a return is filed after 5 years from the last day prescribed for filing the return or after 1 year from the date of the overpayment, whichever period is later, unless before the expiration of the period, the taxpayer files a claim or the department of revenue has determined the existence of the overpayment and has approved the refund or credit. If the taxpayer has agreed in writing under the provisions of subsection (1) to extend the time within which the department may propose an additional assessment, the period within which a claim for refund or credit may be filed or a credit or refund allowed if a claim is not filed is automatically extended.
(3) If a return is required to be filed and the taxpayer fails to file the return, the tax may be assessed or an action to collect the tax may be brought at any time. If a return is required to be filed and the taxpayer files a fraudulent return, the 5-year period provided for in subsection (1) does not begin until discovery of the fraud by the department.