Wis. Stat. § 76.075
Within 4 years after the due date, or extended due date, of the report under s. 76.04, any person subject to taxation under this subchapter may request the department to make, or the department may make, an adjustment to the data under s. 76.07 (4g) or (4r) submitted by the person. If an adjustment under this section results in an increase in the tax due under this subchapter, the person shall pay the amount of the tax increase plus interest on that amount at the rate of 1 percent per month from the due date or extended due date of the report under s. 76.04 until the date of final determination and interest at the rate of 1.5 percent per month from the date of final determination until the date of payment. If an adjustment under this section results in a decrease in the tax due under this subchapter, the department shall refund the appropriate amount plus interest at the rate of 0.25 percent per month from the due date or extended due date under s. 76.04 until the date of refund. Sections 71.74 (1) and (2) and 71.75 (6) and (7), as they apply to income and franchise tax adjustments, apply to adjustments under this section. Review of the adjustments is as stated in s. 76.08.
Wis. Stat. § 76.075