Rents and royalties from real or tangible personal property, capital gains, interest, dividends, or patent or copyright royalties, to the extent that they constitute nonapportionable income, must be allocated as provided in Article IV, subsections (4) through (8), of 15-1-601.
Allocation Of Nonapportionable Income
Mont. Code Ann. § 15-31-304, under Allocation and Apportionment of Income.
Mont. Code Ann. § 15-31-304