Wis. Stat. § 73.0305

The department of revenue shall determine and certify to the state superintendent of public instruction, at the superintendent’s request, the allowable rate of increase under subch. VII of ch. 121. The allowable rate of increase is the percentage change, if not negative, in the consumer price index for all urban consumers, U.S. city average, between the preceding March 31 and the 2nd preceding March 31, as computed by the federal department of labor.