Mont. Code Ann. § 61-3-311

Registration – time periods

(1) Unless a motor vehicle, trailer, semitrailer, or pole trailer is subject to permanent registration under this title and except as provided in 61-3-313, 61-3-701, 61-3-721, and subsection (3) of this section, the department, an authorized agent, or a county treasurer shall, upon original registration of a motor vehicle in this state, assign each motor vehicle to a registration period, as provided in 61-3-316, based upon the calendar month in which the motor vehicle is first registered in this state and designate the calendar year in which the current registration will expire.

(2) Each registration period commences on the first day of the calendar month in the calendar year in which the motor vehicle is registered and the motor vehicle's registration expires on the earlier of:

(a) the last day of the month preceding the anniversary of the registration period for the year designated on the motor vehicle's registration decal if the motor vehicle is registered for a minimum 12-month period;

(b) the last day of the month preceding the anniversary of the registration period for the year designated on the motor vehicle's registration decal if the motor vehicle is registered for a period of at least 13 but less than 25 months; or

(c) the transfer of ownership of the motor vehicle, trailer, semitrailer, or pole trailer to another person.

(3) (a) Upon request of the motor vehicle owner, a county treasurer or an authorized agent may assign a motor vehicle to a registration period, as provided in 61-3-316, other than a registration period beginning in the calendar month in which the motor vehicle is first registered in this state if at least 13 but less than 25 months will elapse between the first day of the calendar month in which the motor vehicle is registered and the last day of the month preceding the anniversary of the requested registration period in the year designated on the motor vehicle's registration decal.

(b) The county treasurer or an authorized agent shall determine fees imposed for a motor vehicle registered for a period between 13 and 24 months. All registration fees, fees in lieu of tax, or local option taxes or fees that are imposed on an annual basis must be prorated based on the number of months in the requested registration period.

(c) A motor vehicle registered under the provisions of 61-3-303(4)(b) may not be registered under this subsection (3).

(4) If a motor vehicle, trailer, semitrailer, or pole trailer is permanently registered under the provisions of this chapter, the registration is not subject to expiration unless the registered owner of the motor vehicle, trailer, semitrailer, or pole trailer transfers ownership of the vehicle to another person.