A bank is under no obligation to a customer having a checking account to pay a check, other than a certified check, which is presented more than 6 months after its date, but it may charge its customer's account for a payment made thereafter in good faith.
Bank Not Obligated To Pay Check More Than 6 Months Old
Mont. Code Ann. § 30-4-404, under Relationship Between Payor Bank and Its Customer.
Mont. Code Ann. § 30-4-404