Why doesn’t the amount in Box 5 (Medicare wages) match the total Gross Earnings on my last payslip of the year?

The W-2 Box 5 amount is taxable wages subject to Medicare taxes. This differs from your gross earnings because there are certain deductions that reduce your Medicare taxable wages, such as pretax medical/dental and vision insurance, and FSA Medical and Dependent Care. Retirement deposits and Tax-Deferred Savings Plans do not reduce your Medicare taxable wages. Medicare taxable wages do not have a cap amount in the year.