Idaho Code § 49-437: Increase in maximum gross weight — Fees for remaining portion of year.

(1) When a motor vehicle registered under section 49-434 or 49-435, Idaho Code, has once been registered and during the year of that registration increases the maximum gross weight, the higher fee due for the weight increase shall be offset by the fee already paid. The fee already paid and the fee due shall be prorated by one-twelfth (1/12) for each month already expired in the registration period. The difference between the two (2) fees shall be the balance due for the remainder of the registration period. If an owner changes the weight during a registration period, the weight change shall not result in a refund of the fees already paid.

(2) If a motor vehicle is not operated on any highway during the first months of a registration period, the owner may at any time thereafter be registered for the remainder of the registration period on payment of all fees, rounded to the nearest whole dollar, as provided in this chapter, less one-twelfth (1/12) of such fees for each full calendar month which has expired prior to registering, but in no event shall the minimum fee be less than five dollars ($5.00).