Employers who expect to receive updated W-4 forms from employees using the 2024 IA-W-4 form, but who have not yet received the updated W-4 form, may temporarily use $40 as the total allowance amount and $0 as the additional withholding amount when calculating these employees’ withholding amounts.
Alternatively, for employees who have furnished Form W-4 in any year before 2024, employers may continue to compute withholding based on the information from the employee's most recently furnished Form W-4 but, if they do, must make the following modification: Multiply the number of allowances claimed on line 6 of the pre-2024 W-4 by $40 to determine the amount of allowances. For example, if an employee claims 6 total allowances on a 2023 IA W-4, when calculating the 2024 Iowa withholding the employer should use $240 (6*$40) of total allowances.
Read more about income withholding for tax year 2024.