Indiana Code Title 6. Taxation § 6-6-5.5-10

Sec. 10. (a) A vehicle subject to the International Registration Plan that is registered after the date designated for registration of the vehicle under IC 9-18-2-7 (before its expiration), under IC 9-18.1-13, or under rules adopted by the department shall be taxed at a rate determined by the following formula:

STEP ONE:  Determine the number of months remaining until the vehicle's next registration date.  A partial month shall be rounded to one (1) month.

STEP TWO:  Multiply the STEP ONE result by one-twelfth ( 1/12 ).

STEP THREE:  Multiply the annual excise tax for the vehicle by the STEP TWO product.

(b) A vehicle that is registered with the department under IC 9-18-2-4.6 (before its expiration) or IC 9-18.1-13-3 or the bureau after the date designated for registration of the vehicle under IC 9-18-2-7 (before its expiration) or IC 9-18.1 shall be taxed at a rate determined by the formula set forth in subsection (a).

(c) This subsection applies after December 31, 2016.  A vehicle described in subsection (a) or (b) that has a renewal registration period described in IC 9-18.1-11-3(b) shall be taxed at the annual excise tax rate for the vehicle's current registration period.