The four stacked bars below each show the composition of Medicare revenues. For Medicare Part D and Part B, most of the necessary funds comes from general revenue and premiums. Medicare Part A, however, is funded largely with revenue from payroll taxes. The stacked bar to the far left represents the revenue sources for all three of these parts combined.
2011 Annual Report of the Boards of Trustees of the Federal Hospital Insurance and Federal Supplementary Medical Insurance Trust Funds