Tex. Transportation Code § 502.044

(a) The department shall designate a vehicle registration year of 12 consecutive months to begin on the first day of a calendar month and end on the last day of the 12th calendar month.

(a-1) Notwithstanding Subsection (a), the department shall designate a vehicle registration period of 24 consecutive months to begin on the first day of a calendar month and end on the last day of the 24th calendar month for a passenger car or light truck that:

(1) is sold in this state or purchased by a commercial fleet buyer described by Section 501.0234(b)(4) for use in this state;

(2) has not been previously registered in this or another state; and

(3) on the date of sale is of the current or preceding model year.

(b) The department shall designate vehicle registration years so as to distribute the work of the department and the county assessor-collectors as uniformly as possible throughout the year. The department may establish separate registration years for any vehicle or classification of vehicle and may adopt rules to administer the year-round registration system.

(c) The department may designate a registration period of less than 12 months to be computed at a rate of one-twelfth the annual registration fee multiplied by the number of months in the registration period. The board by rule may allow payment of registration fees for a designated period not to exceed the amount of time determined by department rule.

(d) The department shall issue a registration receipt and registration insignia that are valid until the expiration of the designated period.

(e) The department shall use the date of sale of the vehicle in designating the registration period for a vehicle for which registration is applied under Section 501.0234.