Form W-2 Box 12: Deferred Compensation and Other Compensation. There are several types of compensation and benefits that can be reported in Box 12. Box 12 will report a single letter or double letter code followed by a dollar amount. Here are the codes for Box 12:
 

• Code A – Uncollected Social Security or RRTA tax on tips. Include this amount as part of your total tax on Form 1040.
• Code B – Uncollected Medicare tax on tips. Include this amount as part of your total tax on Form 1040.
• Code C – Taxable benefit of group term-life insurance over $50,000. Already included as part of your taxable wages in Boxes 1, 3, and 5.
• Code D – Non-taxable elective salary deferrals to a 401(k) or SIMPLE 401(k) retirement plan.
• Code E – Non-taxable elective salary deferrals to a 403(b) retirement plan.
• Code F – Non-taxable elective salary deferrals to a 408(k)(6) SEP retirement plan.
• Code G – Non-taxable elective salary deferrals and non-elective employer contributions to a 457(b) retirement plan.
• Code H – Non-taxable elective salary deferrals to a 501(c)(18)(D) tax-exempt plan.
• Code J – Non-taxable sick pay. This amount is not included in taxable wages in Boxes 1, 3, or 5.
• Code K – Excise tax (equal to 20%) on excess "golden parachute" payments. Include this amount as part of your total tax on Form 1040.
• Code L – Non-taxable reimbursements for employee business expenses.
• Code M – Uncollected Social Security or RRTA tax on taxable group term life insurance over $50,000 for former employees. Include this amount as part of your total tax on Form 1040.
• Code N – Uncollected Medicare tax on taxable group term life insurance over $50,000 for former employees. Include this amount as part of your total tax on Form 1040.
• Code P – Non-taxable reimbursements for employee moving expenses, if the amounts were paid directly to the employee.
• Code Q – Non-taxable combat pay. Some individuals may elect to include combat pay when calculating their Earned Income Credit.
• Code R – Employer contributions to an Archer Medical Savings Account. This amount should be reported on IRS Form 8853.
• Code S – Non-taxable salary deferral to a 408(p) SIMPLE retirement plan.
• Code T – Employer paid adoption benefits. This amount is not included in Box 1 wages. You must use IRS Form 8839 to calculate the taxable and non-taxable portion of these adoption benefits.
• Code V – Income from the exercise of non-statutory stock options. This amount is already included as taxable income in Boxes 1, 3, and 5. See also, how to report stock options.
• Code W – Employer contributions to your Health Savings Account. Report this amount on IRS Form 8889.
• Code Y – Salary deferrals under 409A non-qualified deferred compensation plan.
• Code Z – Income received under 409A non-qualified deferred compensation plan. This amount is already included in taxable wages in Box 1. This amount is subject to an additional tax of 20% plus interest as part of your total tax on Form 1040.
• Code AA – After-tax contributions to a Roth 401(k) retirement plan.
• Code BB – After-tax contributions to a Roth 403(b) retirement plan