in 2010, medicare provided health insurance to 48 million americans—40 million people age 65 and older and eight million younger people with disabilities. it was the primary payer for an estimated 15.3 million inpatient stays in 2011, representing 47.2 percent ($182.7 billion) of total aggregate inpatient hospital costs in the united states. on average, medicare covers about half (48 percent) of health care costs for enrollees. medicare enrollees must cover the rest of the cost. these out-of-pocket costs vary depending on the amount of health care a medicare enrollee needs. they might include uncovered services—such as long-term, dental, hearing, and vision care—and supplemental insurance.