Mont. Code Ann. § 15-30-2104 — Tax On Nonresident

15-30-2104 . Tax on nonresident. (1) (a) Except as provided in 15-30-2106 , a tax is imposed on each nonresident individual, estate, or trust equal to the tax computed under 15-30-2103 as if the nonresident individual, estate, or trust were a resident during the entire tax year, multiplied by the ratio of Montana source income to total income from all sources.
(b) This subsection (1) does not permit any items of income, gain, loss, deduction, expense, or credit to be counted more than once in determining the amount of Montana source income, and the department may adopt rules that are reasonably necessary to prevent duplication or to provide for allocation of particular items of income, gain, loss, deduction, expense, or credit.
(2) Pursuant to the provisions of Article III, section 2, of 15-1-601 , each nonresident taxpayer required to file a return and whose only activity in Montana consists of making sales and who does not own or rent real estate or tangible personal property within Montana and whose annual gross volume of sales made in Montana during the taxable year does not exceed $100,000 may elect to pay an income tax of 1/2 of 1% of the dollar volume of gross sales made in Montana during the taxable year. The tax is in lieu of the tax imposed under 15-30-2103 and subsection (1)(a) of this section. The gross volume of sales made in Montana during the tax year must be determined according to the provisions of Article IV, sections 11 and 12, of 15-1-601 .