How Form W-4 affects your paycheck withholding
The information you provide determines how much comes out of each paycheck. Key details included on your W-4 include:
- Filing status
- Other jobs
- Dependents
- Any extra income or deductions
Generally, withholding should be close to your actual tax liability for the year, so that when you file, you owe little or get a small refund rather than a big surprise in either direction. If your withholding is significantly different from your actual tax liability, it could result in:
- Under-withholding: Too little is taken out, so you owe a balance when you file. If you don’t meet the safe-harbor threshold (your withholding covered 90% or more of your tax liability, or 100% of last year’s liability (110% if your prior-year adjusted gross income was over $75,000, $150,000 if married filing jointly), you may owe penalties.
- Over-withholding: Too much is taken out, meaning you get a larger refund, but you’ve effectively given the IRS an interest-free loan with your own money all year.
How to fill out Form W-4
- Part 1 - Step 1: Personal information (completed by everyone)
- Part 2 - Steps 2 -4: Optional (completed only if it applies)
- Multiple jobs or working spouse
- Dependent credits
- Other income, deductions, and extra withholding
- Part 3 - Step 5: Signature (completed by everyone)
Note: Steps 2 through 4 are optional and only apply if they’re relevant to you—someone with one job, no dependents, and no extra income can complete just Steps 1 and 5 and still end up with reasonably accurate withholding.
When you should submit a new W-4
Update your W-4 whenever a major life change affects your tax situation:
- Getting married or divorced
- Having or adopting a child
- Starting or leaving a second job, or picking up freelance income
- A significant raise, bonus, or drop in income
- Noticing you owed a lot, or got an unusually large refund, the previous year
The IRS Tax Withholding Estimator walks you through your specific numbers and tells you exactly what to put on a new form, rather than guessing.
Note: Your W-4 never goes to the IRS. Your employer keeps it on file and uses it purely to calculate your paycheck withholding—the IRS only sees the results, reported later on your W-2.
Common W-4 mistakes to avoid
- Forgetting to update your W-4 after a life change: A stale W-4 based on your situation from years ago is one of the most common reasons people owe unexpectedly.
- Mishandling the multiple-jobs section: Step 2 has three options (using the IRS’s online estimator, a worksheet, or a simpler checkbox for two similarly paying jobs), and picking the wrong one is a frequent source of under-withholding.
- Claiming exempt when you don’t qualify: Exempt status means no federal income tax is withheld at all—only appropriate if you had no tax liability last year and expect none this year. Claiming it incorrectly can leave you with a large bill at filing time. Note that you must re-file a W-4 by mid-February for every year you claim that you are exempt.
- Ignoring other withholding on your paycheck: Form W-4 only controls federal income tax. It has no effect on FICA taxes withheld from every paycheck, which fund Social Security and Medicare, and are calculated separately at a fixed rate.
