Mont. Code § 72-16-905
The tax imposed upon the transfer of each estate is equal to the maximum tax credit allowable for state death taxes against the federal estate tax imposed with respect to the portion of the decedent's estate having a taxable situs in this state. It is the purpose and intent of this part to impose only those additional taxes that may be necessary to give this state the full benefit of the maximum tax credit allowable against the federal estate tax imposed with respect to a decedent's estate that has a taxable situs in this state. If only a portion of a decedent's estate has a taxable situs in this state, the maximum tax credit must be determined by multiplying the entire amount of the credit allowable against the federal estate tax for state death taxes by the percentage that the value of the portion of the decedent's estate that has a taxable situs in this state bears to the value of the entire estate.
§ 72-16-905, MCA