Why Are Box 1 and Box 3 Different on Your W-2?

Box 1 and Box 3 on a W-2 are different because they report wages for two separate taxes that follow different rules. Box 1 is your federal income tax wages, and it drops when you make pre-tax retirement contributions. Box 3 is your Social Security wages, which include those retirement contributions but stop counting once your pay hits the annual wage cap of $184,500 for 2026.¹ Almost every gap between the two boxes comes down to one of those two things.

What Each Box Is Actually Reporting

Box 1 shows wages, tips, and other compensation subject to federal income tax. It’s the figure that flows onto Form 1040, Line 1a.² Several pre-tax payroll items reduce it before your employer prints the W-2.

Box 3 shows wages subject to the 6.2% Social Security tax. The rules for what belongs in Box 3 aren’t the same as the rules for Box 1, and that’s the whole reason the two numbers rarely match.

The Usual Reason for the Gap: Traditional 401(k) or 403(b) Contributions

For most workers, the difference is a traditional retirement plan deferral. When you send part of your salary to a traditional 401(k) or 403(b) on a pre-tax basis, that money drops out of Box 1. You don’t owe federal income tax on it until you withdraw it later.³

Social Security tax works differently. The IRS requires employers to include pre-tax elective deferrals, after-tax contributions, and designated Roth contributions when calculating Social Security wages.⁴ So the same $10,000 that vanishes from Box 1 stays right where it was in Box 3.

Here’s how that looks in practice. Someone earning $80,000 who contributes $10,000 to a traditional 401(k) and pays $4,000 in pre-tax health insurance premiums through a Section 125 cafeteria plan would see:

Box 1: $66,000 ($80,000 minus the $10,000 401(k) deferral minus the $4,000 in premiums)
Box 3: $76,000 ($80,000 minus only the $4,000 in premiums)

The $10,000 gap matches the 401(k) deferral exactly. Your employer reports the deferral amount in Box 12: Code D for a 401(k), Code E for a 403(b).⁵

The deferral isn’t tax-free, only tax-deferred. Income tax gets paid at withdrawal. Social Security and Medicare taxes get paid now, which is why the wages still count for Box 3.³

The Other Reason: You Earn Above the Social Security Wage Cap

Social Security tax only applies up to an annual wage base. For 2026 that ceiling is $184,500.⁶ Once your wages from a single employer hit that number, the employer stops adding to Box 3 and stops withholding Social Security tax. Box 1 keeps climbing with every additional dollar you earn.

An executive earning $275,000 with no pre-tax deductions affecting Box 1 would see Box 1 at $275,000 and Box 3 at $184,500. The gap is $90,500, and it exists because federal income tax has no wage cap while Social Security tax does.

If you earn well above the cap and also make large traditional 401(k) contributions, the two boxes can end up unexpectedly close. The deferral pulls Box 1 down; the cap pulls Box 3 down. In that situation Box 1 can even come out lower than Box 3, which surprises people who assume Box 3 is always the bigger number.

Deductions That Don’t Create a Gap

Not every pre-tax deduction produces a difference. Benefits elected under a Section 125 cafeteria plan, including pre-tax health insurance premiums and flexible spending account contributions, are excluded from both federal income tax wages and Social Security wages.⁷ They come out of Box 1 and Box 3 in equal amounts.

HSA contributions made through a cafeteria plan work the same way. They’re excluded from gross income and don’t show up in Box 1 or Box 3.⁸

So if your only pre-tax deductions are health premiums or FSA contributions run through a cafeteria plan, and your total pay is under the wage base, Box 1 and Box 3 should be identical.

Roth 401(k) and Roth 403(b) Contributions

Roth deferrals are made with after-tax dollars. They stay in Box 1, and they also stay in Box 3.⁴ They create no gap. If you switched from a traditional 401(k) to a Roth 401(k) partway through the year, expect the difference between the two boxes to shrink. Roth deferrals appear in Box 12 under Code AA (Roth 401(k)) or Code BB (Roth 403(b)).⁵

Group-Term Life Insurance Over $50,000

If your employer provides more than $50,000 of group-term life insurance, the imputed cost of the excess coverage gets added to Box 1, Box 3, and Box 5 in equal amounts, and appears in Box 12 under Code C.⁹ Because it hits both boxes equally, it doesn’t create a gap on its own. It can explain why Box 1 is a little higher than you expected after subtracting your pre-tax deductions from your gross salary.

How to Check Your Own W-2

Start with Box 12. The codes there tell you what moved between the boxes:

Code D: traditional 401(k) deferral
Code E: traditional 403(b) deferral
Code AA: Roth 401(k) deferral
Code BB: Roth 403(b) deferral
Code W: HSA contributions through a cafeteria plan
Code C: taxable cost of group-term life insurance over $50,000

If your only Box 12 entry is Code D or Code E, add that amount to Box 1. The result should land at or very close to Box 3 (assuming you’re under the wage base cap). If it does, the W-2 is doing exactly what it’s supposed to do.¹⁰

If you earn above $184,500 from a single employer, Box 3 should show exactly $184,500 and no more. A single employer’s Box 3 should never exceed the wage base cap. If it does, ask your payroll department to take another look.

Quick Summary of What Reduces Which Box

Traditional 401(k) or 403(b) deferral: reduces Box 1 only. Box 3 stays higher.
Roth 401(k) or 403(b) deferral: reduces neither box.
Pre-tax health insurance premiums (Section 125): reduces both boxes equally.
FSA contributions (Section 125): reduces both boxes equally.
HSA contributions through a cafeteria plan: reduces both boxes equally.
Group-term life insurance over $50,000: increases both boxes equally.
Earnings above $184,500: included in Box 1, excluded from Box 3.

1
Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates
2
Internal Revenue Service. Form 1040
3
Internal Revenue Service. Topic No. 424, 401(k) Plans
4
Internal Revenue Service. Retirement Plan FAQs Regarding Contributions
5
Internal Revenue Service. General Instructions for Forms W-2 and W-3 (2026)
6
Social Security Administration. 2026 Cost-of-Living Adjustment (COLA) Fact Sheet
7
Office of the Law Revision Counsel. 26 USC 125 – Cafeteria Plans
8
Internal Revenue Service. Publication 969 (2025), Health Savings Accounts and Other Tax-Favored Health Plans
9
Internal Revenue Service. Employer’s Tax Guide to Fringe Benefits
10
Internal Revenue Service. Common Errors on Form W-2 Codes for Retirement Plans