A W-4 Form is a document that employees in the United States fill out to inform their employer about how much federal income tax to withhold from their paychecks. This form helps ensure that the correct amount of tax is deducted based on the employee's financial situation, including their marital status and number of dependents. Employees can update their W-4 Form whenever their personal circumstances change, such as getting married, having a child, or starting a new job. Properly completing this form can help prevent owing a large tax bill at the end of the year or receiving a large refund.