Updated September 29, 2026. Quick answer: code S in Box 12 is the amount you deferred from your pay into an employer SIMPLE IRA. If the SIMPLE plan is part of a 401(k) arrangement, the IRS says to use code D instead.
What the IRS tells the employer
The instructions define code S as “Employee salary reduction contributions under a section 408(p) SIMPLE plan (this includes salary reduction contributions made to a Roth SIMPLE IRA).” and continue: “Show deferrals under a section 408(p) salary reduction SIMPLE retirement account. However, if the SIMPLE plan is part of a section 401(k) arrangement, use code D.”
Roth SIMPLE amounts
The Box 1 list of taxable items includes “Salary reduction contributions made to a Roth IRA pursuant to a SEP arrangement or SIMPLE IRA plan.” Box 3 also lists code S among the deferral codes it covers.
Related SEP code
Salary reduction SEP deferrals have their own code. The instructions give code F to “Elective deferrals under a section 408(k)(6) salary reduction SEP”. A SIMPLE inside a 401(k) uses code D.
Common mistakes
- Using S when the SIMPLE sits inside a 401(k). The instruction sends those deferrals to code D.
- Looking for the amount inside Box 1. Elective deferrals other than designated Roth amounts are excluded from it.
Related: code D, code E, code G, code H, and the SIMPLE IRA contribution limit.
Every code in one place: the Box 12 codes table. If a withdrawal from one of these accounts is your question, see the Form 1099-R Box 7 codes.
Figures verified against the IRS 2026 General Instructions for Forms W-2 and W-3 on September 30, 2026.
Sources
- IRS, 2026 General Instructions for Forms W-2 and W-3: https://www.irs.gov/pub/irs-pdf/iw2w3.pdf
- IRS, About Form W-2, Wage and Tax Statement: https://www.irs.gov/forms-pubs/about-form-w-2
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How our partner relationships workCode meanings are read from the IRS 2026 General Instructions for Forms W-2 and W-3 (Box 12) at irs.gov on September 29, 2026. General information, not tax advice. Your own facts decide the outcome, and a payroll professional, a preparer or the IRS is the right place to confirm anything consequential.