Mont. Code § 31-1-243
The holder of a contract, upon request by the buyer, may extend the scheduled due date of all or any part of any installment or installments or defer payment or payments or renew or restate the unpaid time balance of the contract, the amount of the installments, and the time schedule for the installments and may collect for the extension, deferment, renewal, or restatement a refinance charge. The holder may compute the refinance charge on the unpaid time balance to be extended, deferred, renewed, or restated by adding to the unpaid time balance the cost for any insurance and other benefits incidental to the refinancing plus any accrued delinquency and collection charges, after deducting any refund that may be due the buyer as for a prepayment pursuant to 31-1-242 at the rate of the finance charge specified in 31-1-241. If all unpaid installments are deferred for not more than 2 months, the holder may charge and collect for the deferment an amount equal to the difference between the refund required for prepayment in full under 31-1-242 as of the scheduled due date of the first deferred installment and the refund required for prepayment in full as of 1 month prior to the date, times the number of months in which a scheduled payment is not made.
§ 31-1-243, MCA