Mont. Code Ann. § 32-1-453

Interest or commissions unpaid, although due or accrued, on debts owing to any bank may not be included in calculation of its profits, unless the bank keeps its books on a complete accrual basis in which event the bank shall show on its books accrued interest receivable on notes, bonds, and other investments, unless the same is past due, and shall also carry on its books accrued interest, taxes, and expenses payable.