What Does Box 12 Code A Mean on a W-2?
Uncollected Social Security tax on tips — what it means, whether it's taxable, and what to do with it.
By the Easy Guides Editorial Team · Updated for 2026
Code A in Box 12 of your W-2 means uncollected social security tax on tips. Tax treatment: You may owe it.
What Code A means
It usually shows up when your tip income was large relative to your regular wages, so there wasn't enough pay to withhold the full Social Security tax.
Does Code A affect my taxes?
This is Social Security tax on your tips that your employer couldn't collect from your paychecks. You owe it — it's added to your total tax on Schedule 2 of your return.
Where to find Code A 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: A 5,000" means Code A with a $5,000 amount. When you file, enter the code and amount exactly as shown.