What Does Box 12 Code B Mean on a W-2?
Uncollected Medicare 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 B in Box 12 of your W-2 means uncollected medicare tax on tips. Tax treatment: You may owe it.
What Code B means
It appears for the same reason as Code A — high tips relative to regular wages left too little to withhold the full Medicare tax.
Does Code B affect my taxes?
This is Medicare tax on tips your employer couldn't collect from your pay. Like Code A, you owe it and it's added to your total tax on Schedule 2.
Where to find Code B 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: B 5,000" means Code B with a $5,000 amount. When you file, enter the code and amount exactly as shown.