Mont. Code Ann. § 15-53-145
Deficiency assessment -- review -- interest -- penalty
15-53-145 . Deficiency assessment -- review -- interest -- penalty. (1) If the department determines that the amount of tax due is greater than the amount reported, it shall mail to the taxpayer a notice, pursuant to 15-1-211 , of the additional tax proposed to be assessed. The taxpayer may seek a review of the determination pursuant to 15-1-211 .
(2) Penalty and interest must be added to any deficiency assessment as provided in 15-1-216 .