Ask Rusty – Is the Medicare Part B Premium a Percentage of our Social Security Amount? Dear Rusty: I have a simple question: Is the amount we pay for Medicare Part B premium a percent of our Social Security amount we receive? Signed: Curious Dear 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. Conversely, those with a higher “provisional income” (an IRS definition), may pay more than the standard Medicare Part B premium.