Wisconsin Statutes Taxation (Ch. 70 to 79) § 71.84. Addition to the tax

(2) Corporations.(a) Except as provided in s. 71.29(7), in the case of any underpayment of estimated tax by a corporation under s. 71.29 or 71.48, there shall be added to the aggregate tax for the taxable year interest at the rate of 12 percent per year on the amount of the underpayment for the period of the underpayment.In this paragraph, “period of the underpayment” means the time period from the due date of the installment until either the date on which the corporation is required to file for federal income tax purposes, not including any extension, under the Internal Revenue Code or the date of payment, whichever is earlier. If 90 percent of the tax shown on the return is not paid by the date on which the corporation is required to file for federal income tax purposes, not including any extension, under the Internal Revenue Code, the difference between that amount and the estimated taxes paid, along with any interest due, shall accrue delinquent interest under s. 71.91(1)(a).

(b) For corporations that are subject to a tax under this chapter on unrelated business taxable income, as defined under section 512 of the internal revenue code, and virtually exempt entities, “period of the underpayment” means the time period from the due date of the installment until either the 15th day of the 5th month beginning after the end of the taxable year or the date of payment, whichever is earlier. If 90 percent of the tax shown on the return is not paid by the 15th day of the 5th month following the close of the taxable year, the difference between that amount and the estimated taxes paid along with any interest due, shall accrue delinquent interest under s. 71.91(1)(a).

(c) If a refund under s. 71.29(3m) results in an income or franchise tax liability that is greater than the amount of estimated taxes paid when reduced by the amount of the refund, the taxpayer shall add to the aggregate tax for the taxable year interest at an annual rate of 12 percent on the amount of the unpaid tax liability for the period beginning on the date the refund is issued and ending on either the date on which the taxpayer is required to file for federal income tax purposes, not including any extension, under the Internal Revenue Code or the date the tax liability is paid, whichever is earlier.