What Does Box 12 Code D Mean on a W-2?

401(k) contribution (traditional, pre-tax) — what it means, whether it's taxable, and what to do with it.

By the Easy Guides Editorial Team · Updated for 2026

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Quick answer

Code D in Box 12 of your W-2 means 401(k) contribution (traditional, pre-tax). Tax treatment: Pre-tax (already excluded).

What Code D means

The amount counts toward the annual 401(k) contribution limit. If you changed jobs, add up Code D from every W-2 to check you didn't over-contribute.

Does Code D affect my taxes?

This is what you put into a traditional 401(k) through payroll. It's already left out of your Box 1 taxable wages — that's the tax break — so you don't deduct it again.

Where to find Code D on your W-2

Box 12 has up to four slots — labeled 12a, 12b, 12c, and 12d. Each slot shows a letter code and a dollar amount. The 12a–12d labels are just line numbers; the actual code is the small letter next to the money. So "12a: D 5,000" means Code D with a $5,000 amount. When you file, enter the code and amount exactly as shown.

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Frequently asked questions

This is what you put into a traditional 401(k) through payroll. It's already left out of your Box 1 taxable wages — that's the tax break — so you don't deduct it again.
Enter the code and amount into your tax software exactly as they appear on the W-2. The software handles the rest — you don't calculate anything by hand.
Box 12 has up to four slots labeled 12a, 12b, 12c, and 12d. Each slot holds a letter code and a dollar amount. The small letter (like D) is the code; the number next to it is the amount. The 12a–12d labels are just line labels, not codes.

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