Medicare is federal health insurance mainly for people 65 and older and some younger people with disabilities. It is divided into parts that cover hospital care, doctor visits, and prescription drugs, and you choose how to combine those parts for your coverage.

Basic structure

Medicare has four main parts: Part A (hospital), Part B (medical), Part C (Medicare Advantage), and Part D (prescription drugs). Parts A and B together are called “Original Medicare,” while Part C is an alternative way to get A and B (usually plus drugs) through private plans approved by the government.

Original Medicare (Parts A and B)

Part A helps pay for inpatient hospital stays, skilled nursing facility care (under certain conditions), some home health care, and hospice. Part B helps pay for doctor visits, outpatient services, durable medical equipment, and many preventive services like screenings and vaccines. With Original Medicare, you can generally see any provider in the U.S. who accepts Medicare, but there is no annual out-of-pocket limit unless you add other coverage such as a Medigap policy.

Medicare Advantage (Part C)

Medicare Advantage plans are offered by private insurers that bundle Part A and Part B and usually Part D into one plan, often with extra benefits like vision, hearing, or dental. These plans must cover almost all services Original Medicare covers, but they typically use provider networks, may require referrals, and have their own premiums, copays, and an annual out-of- pocket maximum.

Prescription drugs (Part D)

Part D is prescription drug coverage offered by private plans approved by Medicare, available as stand‑alone drug plans with Original Medicare or built into many Medicare Advantage plans. Enrollment is voluntary, but if you delay signing up without having other “creditable” drug coverage, you may pay a late enrollment penalty added to your Part D premium.

Medigap and costs

If you stay with Original Medicare, you can choose a Medigap (Medicare Supplement) policy from a private insurer to help pay deductibles, coinsurance, and other out‑of‑pocket costs because Original Medicare has no yearly spending cap. In general, most people pay no premium for Part A if they paid Medicare payroll taxes long enough, pay a monthly premium for Part B, and may pay additional premiums for Part C, Part D, or Medigap depending on the plan they choose.

Enrollment and eligibility

Most people become eligible for Medicare at age 65, and those already receiving Social Security are usually enrolled automatically in Parts A and B unless they opt out of Part B. Others need to sign up during specific enrollment periods (initial, special, or general), and missing these windows can lead to late penalties or gaps in coverage.