701—307.2(422) Computation of amount withheld.
	307.2(1) Amount withheld.
	a. 	General rules. Every employer required to deduct and withhold a tax on compensation paid in Iowa to an individual shall deduct and withhold for each payroll period an amount the total of which will approximate the employee’s annual tax liability. “Payroll period” for Iowa withholding purposes shall have the same definition as in Section 3401 of the Internal Revenue Code and shall include “miscellaneous payroll period” as that term is defined and used in that section and the associated regulations.
	b. 	Methods of computations. Employers required to withhold Iowa income tax on compensation paid in this state shall compute the amount of tax to be withheld for each payroll period pursuant to the methods and rules provided herein.
	(1)	Tables. An employer may elect to use the withholding tables provided in the Iowa employers’ withholding tax guide and withholding tables, which are available from the department of revenue.
	(2)	Formulas. Formulas that are provided in the Iowa employers’ withholding tax guide and tax tables are available for employers who have a computerized payroll system.
	(3)	Other methods. An employer may request and be granted the use of an alternate method for computing the amount of Iowa tax to be deducted and withheld for each payroll period so long as the alternate proposal approximates the employee’s annual Iowa tax liability. When submitting an alternate formula, the withholding agent should explain the formula and show examples comparing the amount of withholding under the proposed formula with the department’s tables or computer formula at various income levels and by using various numbers of personal exemptions. Any alternate formula must be approved by the department prior to its use.
	c. 	Supplemental wage payments. A supplemental wage payment is the payment of a bonus, commission, overtime pay, or other special payment that is made in addition to the employee’s regular wage payment in a payroll period. When such supplemental wages are paid, the amount of tax required to be withheld shall be determined by using the current withholding tables or formulas. If supplemental wages are paid at the same time as regular wages, the regular tables or formulas are used in determining the amount of tax to be withheld as if the total of the supplemental and regular wages were a single wage payment for the regular payroll period. If supplemental wages are paid at any other time, the regular tables or formulas are used in determining the amount of tax to be withheld as if the supplemental wage were a single wage payment for the regular payroll period. When a withholding agent makes a payment of supplemental wages to an employee and the employer withholds federal income tax on a flat-rate basis, pursuant to Treasury Regulation §31.3402(g)-1, state income tax shall be withheld from the supplemental wages at a rate of 6 percent without consideration for any withholding allowances or exemptions.
	d. 	Vacation pay. Amounts of so-called “vacation allowances” shall be subject to withholding as though they were regular wage payments made for the period covered by the vacation. If the vacation allowance is paid in addition to the regular wage payment for such period, the allowance shall be treated as supplemental wage payments.
	307.2(2) Correction of underwithholding or overwithholding.
	a. 	Underwithholding. If an employer erroneously underwithholds an amount of Iowa income tax required to be deducted and withheld from compensation paid to an employee within a payroll period, the employer should correct the error within the same calendar year by deducting the difference between the amount withheld and the amount required to be withheld from any compensation still owed the employee, even though such compensation may not be subject to withholding. If the error is discovered in a subsequent calendar year, no correction shall be made by the employer.
	b. 	Overwithholding. If an employer erroneously overwithholds an amount of tax required to be deducted and withheld from compensation paid to an employee, repayment of such overwithheld amount shall be made in the same calendar year. Repayment may be made in either of two ways: (1) the amount of overwithholding may be repaid directly to the employee, in which case the employer must obtain written receipt showing the date and amount of the repayment, or (2) the employer may reimburse the employee by applying the overcollection against the tax required to be deducted and withheld on compensation to be paid in the same calendar year in which the overcollection occurred. If the error is discovered in a subsequent calendar year, no repayment shall be made.
This rule is intended to implement Iowa Code section 422.16.
[Editorial change: IAC Supplement 11/2/22]