What are the codes in box 12 on w2?

Box 12 on a W-2 form contains various codes that provide additional information about an employee's earnings and benefits. Each code corresponds to specific types of compensation or deductions, such as retirement plan contributions (e.g., Code D for 401(k) contributions), health insurance premiums, or other fringe benefits. Employers use these codes to report items that may not be included in the standard wages reported in other boxes. Employees should review these codes to understand their tax implications and ensure accurate reporting on their tax returns.