The maximum duration of a standard residential lease agreement in Montana is one (1) year. Lease agreements for a duration longer than one year need to be signed by both landlord and tenant in order to be valid (MT Code § 70-24-204).
Verbal leases are permitted in addition to written leases, but it is recommended that all leases be in writing. Verbal leases are enforceable, but it is more difficult to prove the terms and conditions of an agreement, or if there was an agreement in the first place.
If there is no tenancy duration written into the lease, it is considered a month-to-month lease in most cases (unless rent is paid weekly). (MT Code § 70-24-201 (2019)).
The information for this answer was found on our Montana Residential Lease Agreement answers.