W-2 Box 2 vs. Box 4 vs. Box 6: which withheld tax is which?
The short answer
Your W-2 reports three federal taxes withheld in three different boxes: Box 2 is federal income tax, Box 4 is Social Security tax, and Box 6 is Medicare tax. They are separate taxes with separate rules, and only Box 2 is the "federal withholding" that gets credited against your income tax on a return. The box-by-box definitions come from the IRS General Instructions for Forms W-2 and W-3.
Each withholding box pairs with a wage box
The form is built in pairs — a wage figure, then the tax withheld on it:
- Box 1 → Box 2. Box 1 is taxable wages for income tax. Box 2 is the federal income tax withheld from them.
- Box 3 → Box 4. Box 3 is Social Security wages. Box 4 is the Social Security tax withheld.
- Box 5 → Box 6. Box 5 is Medicare wages. Box 6 is the Medicare tax withheld.
Reading them as pairs explains most of the confusion. Someone comparing Box 2 to Box 5, or Box 4 to Box 1, is comparing unrelated figures. The full tour of the form is in how to read your W-2.
Why the three amounts don't line up
Box 2 varies with your W-4. Federal income tax withholding is a progressive estimate — it depends on filing status, dependent credits, extra-withholding requests, and pay frequency. Two coworkers with identical salaries can have very different Box 2 figures. The mechanics are described under Tax Withholding for Employees and in how paycheck tax withholding works.
Boxes 4 and 6 ignore your W-4 entirely. Social Security and Medicare are withheld at flat statutory rates set in law, from the first dollar of covered wages. Nothing you write on a W-4 changes them.
Box 3 stops; Box 5 doesn't. Social Security wages are subject to an annual wage base limit that is adjusted each year, so Box 3 can be lower than Box 5 for higher earners while Box 5 has no cap. Above a set threshold, an Additional Medicare Tax applies on top of the regular Medicare rate. Because the current-year figures change annually, check the IRS for the amounts in force rather than any number you saw quoted somewhere.
Box 1 differs from Boxes 3 and 5. Pre-tax retirement contributions reduce Box 1 but generally not Boxes 3 and 5, which is why Box 1 is often the smallest of the three wage figures. Publication 525 covers what's included in taxable income, and we work through the gap in why Box 1 doesn't match your gross pay.
Only Box 2 counts as "federal withholding" on a return
This is the practical consequence. When a return asks for federal income tax withheld, it means Box 2. Social Security and Medicare are contributions to those programs, not prepayments of income tax, and they don't get added to Box 2 or credited the same way. Publication 17 is the IRS's general reference on how individual income tax is figured and credited.
That's why a W-2 can show meaningful amounts in Boxes 4 and 6 next to a $0 in Box 2 — the two systems apply different thresholds. We cover that exact pattern in Social Security and Medicare withheld but no federal income tax and why federal income tax withheld is $0 on your W-2.
If a box looks wrong
Compare the W-2 against your final pay stub's year-to-date columns first — they should reconcile, allowing for pre-tax deduction differences. If they don't, the correction runs through your employer, who can issue an amended statement. The IRS outlines the steps in Tax Topic 154, and we describe how that process unfolds in what happens if your W-2 is missing or wrong.