(e) Supplemental wages. If supplemental wages, such as bonuses, commissions, or overtime pay, are paid at the same time as regular wages, the amount of tax to be withheld shall be calculated based on the aggregate amount of supplemental and regular wages, as if it were a single wage payment for the payroll period. If supplemental and regular wages are paid at different times, the employer may calculate the amount of tax to be withheld by aggregating the supplemental wages with either: the regular wages for the current payroll period, or the regular wages for the last preceding payroll period within the same calendar year. If supplemental wages are paid to an employee during a calendar year, for a period which includes two or more consecutive payroll periods, and other wages also are paid during the calendar year, the employer shall calculate the amount of tax to be withheld on the supplemental wages as follows:
(1) Determine the average wage for each payroll period by dividing the sum of the supplemental wages and the other wages paid for the payroll period by the number of payroll periods.(2) To determine the amount of tax to be withheld from each payroll period, treat the average wage calculated in paragraph (1) as the amount of wages paid for the payroll period. The amount of taxes to be withheld shall be calculated by using the tables or formula provided by the department, given the length of the payroll period and the average wage paid for the payroll period.(3) Lastly, from the sum of the taxes computed on the basis of the average wage per payroll period, subtract the sum of the taxes previously withheld or to be withheld from wages, other than supplemental wages, for the payroll periods. The balance, if any, constitutes the amount of the tax to be withheld from the supplemental wages.