Definition: A W-4 form is an IRS document used to calculate the amount of federal income taxes withheld from employees pay. The W-4 form is not filed with your income tax return, but filled out in the workplace. The W-4 form is filled out when an employee begins a new job. However, a new W-4 may be filled out by employees at a later date to change the withholding amount.

The W-4 form requires the employee's name, address, Social Security number, marital status and number of dependents.

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Also Known As: W4 Form, Federal Tax Withholding Form