Mont. Code Ann. § 15-31-404

There must be offset against the alternative corporate income tax imposed for any period the amount of any tax imposed against the corporation for the same period under parts 1, 3, and 5 of this chapter. If taxes, interest, and penalties have been or will be assessed against, paid by, or collected from a corporation under this part and the assessment, payment, or collection should have been made under parts 1, 3, and 5 of this chapter, the taxes, interest, and penalties must be considered as having been assessed, paid, or collected under parts 1, 3, and 5 as of the date they were made.