Your W-4 tells your employer how much federal income tax to take from each paycheck. Get it right and you roughly break even at filing time. Get it wrong and you either owe a surprise bill or lend the government an interest-free loan all year.
The form changed in 2020
The post-2020 W-4 dropped allowances. Instead you fill out steps:
- Step 1: name, filing status, signature
- Step 2: extra withholding if you have more than one job or a working spouse (use the IRS online tool or the multiple-jobs worksheet)
- Step 3: claim dependents via the credit amount
- Step 4: other income not subject to withholding, extra deductions beyond the standard amount, and any extra dollar amount you want withheld
You can submit a new W-4 whenever life changes: marriage, a new job, a child, a raise, or a side business.
Use the IRS estimator first
The IRS Tax Withholding Estimator compares your projected tax to current withholding and tells you which step to adjust. It is the fastest way to stop guessing. Most people should re-check it each year, especially after the annual bracket inflation adjustments.
What employers use on the back end
Employers apply the figures from your W-4 using the methods in IRS Publication 15-T, which has the percentage method and wage-bracket tables for 2026. You do not fill those in; your payroll department does. Your job is to give them an accurate W-4.
Common mistakes
- Leaving Step 2 blank when both spouses work, which under-withholds
- Forgetting to update after a big raise, creating an end-of-year balance due
- Claiming "exempt" when you are not, which stops all withholding
Numbers: why it matters
Say a single filer earns $80,000 and forgot Step 2 after picking up a $20,000 freelance gig. No extra withholding on either job could leave them owing a few thousand at filing, plus possible underpayment penalties. A small extra amount on Line 4(c) smooths it out.
Disclaimer: This article is general educational information, not tax, legal, or investment advice. Dollar amounts come from the 2026 sources listed at the end of this article and may change. Before you act, talk to a licensed CPA, EA, or tax attorney about your own situation.