Mont. Code Ann. § 15-37-108

All license taxes assessed under the provisions of this part become delinquent if not paid on or before midnight of the date that the tax is payable as established for the applicable reporting period in 15-37-105 (1). The department shall add to the amount of delinquent metalliferous mines tax penalty and interest as provided in 15-1-216. The department may waive a late payment penalty as provided in 15-1-206.