(1) NORMAL. (a) In assessing taxes interest shall be added to such taxes at 12 percent per year from the date on which such taxes if originally assessed would have become delinquent if unpaid, to the date on which such taxes when subsequently assessed will become delinquent if unpaid.(b) Except as otherwise specifically provided, in crediting overpayments of income and surtaxes against underpayments or against taxes to be subsequently collected and in certifying refunds of such taxes interest shall be added at the rate of 3 percent per year from the date on which such taxes when assessed would have become delinquent if unpaid to the date on which such overpayment was certified for refund except that if any overpayment of tax is certified for refund within 90 days after the last date prescribed for filing the return of such tax or 90 days after the date of actual filing of the return of such tax, whichever occurs later, no interest shall be allowed on such overpayment. For purposes of this section the return of such tax shall not be deemed actually filed by an employee unless and until the employee has included the written statement required to be filed under s. 71.65(1). However when any part of a tax paid on an estimate of income, whether paid in connection with a tentative return or not, is refunded or credited to a taxpayer, such refund or credit shall not draw interest.(c) Any assessment made as a result of the adjustment or disallowance of a claim for credit under s. 71.07, 71.28 or 71.47 or subch. VIII or IX, except as provided in sub. (2) (c), shall bear interest at 12 percent per year from the due date of the claim.(2) DELINQUENT. (a)Income and franchise taxes. Income and franchise taxes shall become delinquent if not paid when due under ss. 71.03(8), 71.24(9) and 71.44(4), and when delinquent shall be subject to interest at the rate of 1.5 percent per month until paid.(b)Department may reduce delinquent interest. The department shall provide by rule for reduction of interest under par. (a) to 12 percent per year in stated instances wherein the secretary of revenue determines that reduction is fair and equitable.(c)Adjustment to credits. Any assessment made as a result of the disallowance of a claim for credit made under s. 71.07, 71.28 or 71.47 or subch. VIII or IX with fraudulent intent, or of a portion of a claim made under said subchapters or sections that was excessive and was negligently prepared, shall bear interest from the due date of the claim, until refunded or paid, at the rate of 1.5 percent per month.(d)Withholding tax. Of the amounts required to be withheld any amount not deposited or paid over to the department within the time required shall be deemed delinquent and deposit reports or withholding reports filed after the due date shall be deemed late. Delinquent deposits or payments shall bear interest at the rate of 1.5 percent per month from the date deposits or payments are required under this section until deposited or paid over to the department. The department shall provide by rule for reduction of interest on delinquent deposits to 12 percent per year in stated instances wherein the secretary of revenue determines reduction fair and equitable. In the case of a timely filed deposit or withholding report, withheld taxes shall become delinquent if not deposited or paid over on or before the due date of the report. In the case of no report filed or a report filed late, withheld taxes shall become delinquent if not deposited or paid over by the due date of the report. In the case of an assessment under s. 71.83(1) (b) 2, the amount assessed shall become delinquent if not paid on or before the first day of the calendar month following the calendar month in which the assessment becomes final, but if the assessment is contested before the tax appeals commission or in the courts, it shall become delinquent on the 30th day following the date on which the order or judgment representing final determination becomes final.Amended by Acts 2013 ch, 20,s 1440e, eff. 7/2/2013.1987 a. 312; 1989 a. 31; 1991 a. 39.