Indiana Code Title 6. Taxation § 6-6-1.6-3

Sec. 3. (a) The department shall calculate an annual index factor to be used for the rate to take effect each July 1 beginning in 2018 through July 1, 2027.  The department shall determine the index factor before June 1 of each year using the method described in subsection (b).

(b) The annual gasoline tax index factor and special fuel index factor equals the following:

STEP ONE:  Divide the annual CPI-U for the year preceding the determination year by the annual CPI-U for the year immediately preceding that year.

STEP TWO:  Divide the annual IPI for the year preceding the determination year by the annual IPI for the year immediately preceding that year.

STEP THREE:  Add:

STEP FOUR:  Divide the STEP THREE result by two (2).

(c) If the CPI-U or IPI for a preceding year is revised, corrected, or updated after May 31 of that year, the department shall use the CPI-U or IPI as published for the preceding year prior to revision.