W-4 (Form W-4)

Form W-4, the Employee's Withholding Certificate, is what you hand your employer so they know how much federal income tax to hold back from each paycheck. Unlike older versions of the form that relied on a simple count of allowances, the current W-4 asks directly about your filing status, whether you hold multiple jobs or your spouse also works, dependents you plan to claim, other income not subject to withholding, and any deductions beyond the standard deduction, plus an option to request extra withholding per paycheck.

You complete a W-4 when you start a new job, and payroll uses your answers to calculate withholding from every subsequent paycheck according to IRS withholding tables. There is no requirement to refile it every year — the settings carry forward until you submit a new one — but you can update it at any time simply by giving your employer a revised form. Married couples with two incomes and taxpayers with multiple jobs should pay particular attention to the multiple-jobs section, since leaving it blank can under-withhold significantly for that household.

A common mistake is filling out a W-4 once at hire and never revisiting it, even after a major life change like marriage, a new child, or picking up a second job — all of which shift the correct withholding amount. Because the form only controls federal withholding at one employer at a time, someone with two jobs needs to think about their combined income across both W-4s, not just what looks correct on either form in isolation, or they risk under-withholding across the household.