What is Form W-4?
Form W-4, Employee's Withholding Certificate, tells your employer how much federal income tax to withhold from your pay. You complete one when you start any job, and you can file a new one with your employer whenever your situation changes — it's not a once-only form.
The modern W-4 (redesigned in 2020) no longer uses "allowances." Instead it works in dollars: you account for multiple jobs, dependents, other income, and extra deductions directly. Most single-job employees only complete Step 1 (identity and filing status) and Step 5 (signature).
Who files Form W-4?
- Every new employee — employers must have one on file to run payroll correctly.
- Anyone whose life changed — marriage, divorce, a new child, a second job, or a side business are all reasons to file a fresh W-4.
- People who owed a big bill or got a big refund last year — both are signs the withholding dial needs adjusting.
Deadlines
No IRS deadline — the W-4 goes to your employer, not the IRS, and takes effect with the next payroll cycle. The IRS releases an updated version each year; existing employees don't have to refile annually, but it's smart to review after any major change or at year-start.
How to fill out Form W-4
Step 1 — personal info and filing status
Name, address, SSN, and whether you file single, jointly, or head of household. For many people this plus a signature is the whole form.
Step 2 — multiple jobs or working spouse
This is the step people skip — and the #1 cause of under-withholding. Use the IRS online estimator or the checkbox if you and/or your spouse hold two jobs of similar pay.
Step 3 — claim dependents
Multiply qualifying children by the credit amount shown on the form, add other dependents, and enter the total.
Step 4 — other income, deductions, extra withholding
Add non-job income (so it's covered by withholding), note itemized deductions beyond the standard, or set a flat extra amount per paycheck.
Step 5 — sign and hand it to your employer
Give it to HR or payroll. Never mail a W-4 to the IRS.