W-2 Box 12 Code D — Elective deferrals to a 401(k) plan

What Box 12 Code D means

Code D reports your traditional, pre-tax elective deferrals to a 401(k) plan — the amount you chose to have withheld from each paycheck and routed into the plan instead of taken as cash. It reduces Box 1 (federal taxable wages) dollar for dollar, which is why your Box 1 total often comes in lower than your Box 3 and Box 5 totals when you defer part of your pay: Social Security and Medicare tax still apply to the full amount before the deferral comes out, and only the federal (and typically state) income tax is postponed until you eventually take a distribution.

The annual §402(g) elective deferral limit caps what you personally can defer across all 401(k) and 403(b) plans combined in a calendar year — it's a per-person cap, not a per-employer or per-plan cap. Employees age 50 and older can defer more under the age-50 catch-up, and SECURE 2.0 layered in a larger catch-up for employees turning 60 through 63 that replaces the standard age-50 amount for that specific age band. A separate §415(c) limit caps total annual additions to the plan — your deferrals plus any employer match or other contributions combined — and sits well above the elective-deferral limit alone.

If you change jobs mid-year, or hold two 401(k)-eligible jobs at once, each employer's payroll system only tracks its own plan and has no visibility into what you deferred somewhere else. That means it's entirely possible to stay under each individual plan's limit while still exceeding your personal §402(g) cap once both W-2s are added together. Excess deferrals identified before the following April 15 can be pulled out as a corrective distribution; left uncorrected, the excess ends up taxed twice — once in the year you deferred it, again when it's eventually distributed.

Code D is strictly the traditional side of the plan. Roth 401(k) contributions — after-tax, already included in Box 1 — are reported separately under code AA, not code D. If your plan offers both and you split your contributions between them, you'll see both codes on the same W-2, and the two amounts share the same overall §402(g) limit even though they're taxed in opposite directions.

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