Form W-4 is a tax form used by employees in the United States to inform their employer about how much federal income tax to withhold from their paychecks. By filling out this form, employees can adjust their withholding based on their personal financial situation, such as marital status and number of dependents. The information provided on Form W-4 helps ensure that employees neither owe a large tax bill at the end of the year nor receive an excessive refund. It is important to review and update this form whenever there are significant life changes, such as a new job or a change in family status.