Social Security Matters: Is The Medicare Part B Premium A Percentage Of Our Social Security Amount? Signed: CuriousDear Curious: Your Medicare Part B premium is not based on a percentage of your monthly Social Security benefit amount. They then divide 25% of total anticipated Part B program costs by the number of expected Part B enrollees, resulting in the “standard” Medicare Part B premium for next year. For those with exceptionally high incomes, the Part B premium can be as much as $690 per month. It presents the opinions and interpretations of the AMAC Foundation’s staff, trained and accredited by the National Social Security Association (NSSA).