What is Form W-4?
A W-4 is the form an employee completes when starting a job so the employer can withhold the right amount of federal income tax. Its full name is the Employee's Withholding Certificate. The employee gives it to the employer, not to the IRS, and the employer keeps it and uses it to calculate withholding. The IRS shows the 2026 version of Form W-4 on its site.
The form was redesigned in 2020 and no longer uses withholding allowances. It has a step-by-step layout. Step 1 asks for personal information and the filing status, Step 2 covers multiple jobs or a working spouse, Step 3 is for claiming dependents and other credits, and Step 4 allows other adjustments, such as other income, deductions, or an extra amount to withhold from each paycheck. Step 5 is the signature. Only Steps 1 and 5 are required, and if the employee leaves the rest blank the employer withholds as if there are no adjustments.
The employer applies the form to the IRS withholding tables (Publication 15-T). A more accurate W-4 means withholding closer to what the person will truly owe. The IRS recommends completing a new one every year and whenever your personal or financial situation changes, for example after marriage, the birth of a child, a second job or a spouse starting or stopping work. The IRS also offers a Tax Withholding Estimator that helps fill in the form.
An employer must put a new W-4 into effect by the start of the first payroll period ending on or after 30 days after receiving it. An employee who does not submit a form is treated as single with no adjustments. The W-4 affects only federal income tax withholding: it has no effect on Social Security or Medicare, which are fixed by FICA. Many states use the same form or their own state withholding certificate.
The W-4 is the reverse of the W-2: the W-4 is the input to withholding at the start of employment, and the W-2 is the summary of what was actually withheld at the end of the year. Employers should keep the W-4 on file, and should never tell an employee how to complete it, since the choices are the employee's own.
In practice
A newly hired employee fills in Step 1 as single and signs, leaving the other steps blank. The employer withholds federal income tax as though the employee has no other jobs or dependents. A year later the employee marries a spouse who also works, so they submit a new W-4, ticking the box in Step 2 and adding a dependent in Step 3. The payroll team enters the change, and the employer must apply it no later than the first payroll period ending on or after the 30th day after it receives the form, though most apply it sooner. The employee later uses the Tax Withholding Estimator, sees they will owe money at filing time, and adds an extra $50 per paycheck in Step 4(c).
Frequently asked questions
What is a W-4 form?
It is the IRS Employee's Withholding Certificate. The employee gives it to the employer so the employer knows how much federal income tax to withhold from each paycheck.
What is a W4 used for?
It is used to calculate federal income tax withholding, based on filing status, other jobs, dependents and any extra withholding. It does not change Social Security or Medicare taxes.
Do I send the federal W-4 to the IRS?
No. The employee gives it to the employer, which keeps it and uses it for payroll. The IRS only asks to see it in certain cases.
When should I update my W-4?
The IRS recommends a new W-4 every year and whenever your personal or financial situation changes, such as marriage, a new child or a second job.
What happens if an employee does not fill in a W-4?
The employer withholds as if the employee is single with no adjustments. That can lead to over-withholding or to a bill at tax time.
What steps are on the W-4?
Step 1 is personal details and filing status, Step 2 is multiple jobs, Step 3 is dependents, Step 4 is other adjustments and Step 5 is the signature. Only Steps 1 and 5 are required.