What Does a W-4 Do? Withholding, Steps, and Updates

A W-4, formally the Employee’s Withholding Certificate, tells your employer how much federal income tax to take out of each paycheck. The details you enter — filing status, dependents, other income, and extra deductions — feed the payroll calculation that determines your withholding every pay period. Fill it out accurately and the amount sent to the IRS across the year lands close to the tax you actually owe, so you avoid both a surprise bill and a paycheck that’s smaller than it needs to be.¹

The Paycheck Lever It Controls

Federal income tax in the United States is pay-as-you-go. Instead of writing one large check in April, you pay a little every payday. Your employer withholds the money and sends it to the IRS in your name. When you file your annual return, the IRS compares what was already withheld against what you actually owe, and you either get a refund or pay the difference.¹

The W-4 is the instruction sheet behind that process. The entries on it tell payroll software which tax rates, standard deduction, and credits to apply each pay period. It doesn’t change how much tax you owe for the year. It only controls the timing — how much of that year’s tax comes out of each paycheck versus how much is settled up when you file.

What Happens If You Skip It

If you start a new job without turning in a W-4, your employer doesn’t stop withholding. They’re required to withhold as if you had selected “Single or Married filing separately” with no adjustments for dependents, other income, or extra deductions.² For many workers, that default pulls more out of each paycheck than necessary. Submitting a completed form lets the withholding reflect credits and deductions you actually qualify for.

What You Tell the Form

The W-4 is organized into four steps plus a signature. Only Step 1 and the signature are required for a valid form. The rest are optional and improve accuracy.³

Step 1: Who You Are and How You File

Your name, address, Social Security number, and filing status — single, married filing jointly, or head of household. Filing status sets your standard deduction and the tax brackets your withholding is based on.¹ For 2026, the standard deduction is $16,100 for single filers, $32,200 for married filing jointly, and $24,150 for head of household.⁴

Step 2: Multiple Jobs or a Working Spouse

Complete this step if you have more than one job or if you’re married filing jointly and your spouse works. Each employer, by default, withholds as if that job is your only income, which usually leaves total withholding short across all your paychecks combined.¹

You have three options: use the IRS Tax Withholding Estimator online, complete the Multiple Jobs Worksheet on the form, or, if there are only two jobs paying roughly the same, check the box in Step 2(c) on both W-4s to split the deduction and brackets in half for each job.

Step 3: Credits for Dependents

If your total household income will be $200,000 or less, or $400,000 or less for married filing jointly, you can claim credits here. For 2026, multiply each qualifying child under 17 by $2,200 and each other dependent by $500.¹ The child amount reflects the 2026 Child Tax Credit of up to $2,200 per qualifying child.⁵ These credits lower what’s withheld each pay period so your take-home more closely matches your after-credit tax bill.

Step 4: Fine-Tuning

Three optional lines let you adjust further:¹

Line 4(a), other income: money you expect that won’t have tax withheld, such as interest, dividends, or retirement distributions. Entering it raises your withholding so you don’t fall short.
Line 4(b), deductions: an estimate of deductions above the standard deduction, which lowers withholding. For 2026, that includes itemized deductions plus the newer deductions for qualified tips, overtime pay, and passenger vehicle loan interest created by the One, Big, Beautiful Bill Act, along with student loan interest and IRA contributions.⁶
Line 4(c), extra withholding: a flat dollar amount added to each paycheck’s withholding. Useful if you have freelance income, investment gains, or simply want a larger refund.

The IRS also runs a free Tax Withholding Estimator at irs.gov/W4App. It walks through your income, deductions, and credits and tells you exactly what to enter on each step, with a slider for how large a refund you’d prefer.⁷ It’s especially useful mid-year, because it can account for months you haven’t worked and adjust the remaining pay periods accordingly.¹

When to Turn One In or Update It

You fill out a W-4 when you start a new job, and you can submit a revised one any time after that.⁸ Common triggers to update:

Marital status changes, which shift your filing status and often your bracket.
A new or lost dependent, worth up to $2,200 in credit per qualifying child.
Starting or leaving a second job, or a spouse’s job changing.
New investment, rental, or retirement income that won’t have tax withheld.
New deductions or credits, like buying a home or paying student loan interest.

If a change reduces the withholding you’re entitled to — a dependent no longer qualifies, for example — you must give your employer a new W-4 within 10 days.⁹ Changes that increase your withholding entitlement have no deadline, but updating sooner puts the benefit in your paycheck sooner.

One special case: if you had no federal income tax liability last year and expect none this year, you can write “Exempt” on your W-4 and no federal income tax will be withheld. The exemption expires annually; to keep it, submit a new W-4 claiming exempt by February 15 of the following year.⁸ Social Security and Medicare are still withheld either way.

How Your W-4 Shows Up at Tax Time

When you file Form 1040, the IRS totals the tax withheld from your paychecks and compares it against what you owe for the year. Overwithheld means a refund. Underwithheld means a balance due.¹ A big refund is money you loaned the government interest-free instead of taking home. A balance due keeps more in your paycheck but has to be settled at filing.

If withholding falls too far short, the IRS can add an underpayment penalty and interest on top of the tax. You generally avoid the penalty by hitting one of these safe harbors:¹⁰

Your withholding and estimated payments cover at least 90% of the current-year tax.
They equal at least 100% of last year’s tax, or 110% if your prior-year adjusted gross income was over $150,000 ($75,000 if married filing separately).
You owe less than $1,000 after subtracting what was withheld.

Most W-2 employees with one job and an accurate W-4 clear these thresholds without doing anything special. Workers with side income, investment gains, or multiple jobs are the ones most likely to come up short, and running the IRS estimator once a year catches problems before the return does.

Federal Only: State Withholding Is Separate

The W-4 handles federal income tax alone. If you live or work in a state with its own income tax, you’ll likely need to fill out a separate state withholding certificate. Nine states have no state income tax and require no additional form. Your employer’s payroll or HR department can tell you which state forms apply, and most digital onboarding systems present the federal and state forms together.

1
Internal Revenue Service. Form W-4 (2026) Employee’s Withholding Certificate
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Internal Revenue Service. Publication 15-T (2026) Federal Income Tax Withholding Methods
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Internal Revenue Service. About Form W-4 Employee’s Withholding Certificate
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Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
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Internal Revenue Service. Child Tax Credit
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Internal Revenue Service. One Big Beautiful Bill Act – Tax Deductions for Working Americans and Seniors
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Internal Revenue Service. Improved Tax Withholding Estimator Helps Workers Target the Refund They Want
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Internal Revenue Service. Topic No. 753 Form W-4 Employees Withholding Certificate
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Internal Revenue Service. Publication 505 Tax Withholding and Estimated Tax
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Office of the Law Revision Counsel. 26 U.S. Code 6654 – Failure by Individual to Pay Estimated Income Tax