Form W-4 is used by employees to determine the correct amount of federal income tax to withhold from their paychecks. It allows employees to claim number of withholding allowances based on their filing status and other situations. The form contains worksheets to help calculate allowances for itemized deductions, credits, two working spouses, and other adjustments to income. Employees provide the completed form to their employer so the proper amount of tax can be withheld from each paycheck.