What's Medicare Part B? 
Part A covers inpatient hospital stays , skilled nursing facility stays , home health visits -LRB- also covered under Part B -RRB- , and hospice care , and accounted for 32 % of benefit spending in 2012 . Part A benefits are subject to a deductible -LRB- $ 1,184 per benefit period in 2013 -RRB- and coinsurance . Part B covers physician visits , outpatient services , preventive services , and home health visits , and accounted for 19 % of benefit spending in 2012 . Part B benefits are subject to a deductible -LRB- $ 147 in 2013 -RRB- , and cost sharing generally applies for most Part B benefits . Part C refers to the Medicare Advantage program , through which beneficiaries can enroll in a private health plan , such as a health maintenance organization -LRB- HMO -RRB- , and receive all Medicare-covered benefits . Payments to Medicare Advantage plans to cover Part A and Part B benefits accounted for 23 % of benefit spending in 2012 . More than 13 million beneficiaries were enrolled in a Medicare Advantage plan in 2012 -LRB- 27 % of all beneficiaries -RRB- . Part D is the voluntary , subsidized outpatient prescription drug benefit , with additional subsidies for beneficiaries with low incomes and modest assets . The Part D benefit is offered through private plans that contract with Medicare , both stand-alone prescription drug plans -LRB- PDPs -RRB- and Medicare Advantage prescription drug plans -LRB- MA-PDs -RRB- . In 2012 , Part D accounted for 10 % of benefit spending . About 32 million beneficiaries were enrolled in a Medicare Part D plan in 2012 . 