Wis. Stat. § 78.015: Annual adjustment of tax rate.

(1) Before April 1 the department shall recompute and publish the rate for the tax imposed under s. 78.01 (1). The new rate per gallon shall be calculated by multiplying the rate in effect at the time of the calculation by the amount obtained under sub. (2). After the calculation of the rate that takes effect on April 1, 2006, the department shall make no further calculation under this subsection and sub. (2).

(2) Divide the annual average U.S. consumer price index for all urban consumers, U.S. city average, as determined by the U.S. department of labor, for the previous year by that annual average for the year before the previous year.

(4) The rate calculated under this section shall be rounded to the nearest 0.1 cent.

(5) The rate calculated under this section is effective on the April 1 after the calculation.