Q & A – An employee submitted a new W-4 and made it retroactive. Do I have to go back and recalculate the withholding on the employee’s prior paychecks?

Q: An employee submitted a new W-4 and made it retroactive. Do I have to go back and recalculate the withholding on the employee’s prior paychecks?

A: An amended W-4 filed by a current employee because of a change in withholding allowances must be put into effect by the employer no later than the beginning of the first payroll period ending on or after the 30th day after the form is filed with the employer [IRC 3402(f)(3)(B)(i)].  The employer may put an amended W-4 into effect earlier than required (e.g., upon receipt), but is not obligated to honor a retroactively amended W-4.