Medicare basics
Medicare Explained: Parts A, B, C and D
Medicare is federal health insurance for people 65 and older and some younger people with disabilities. Here’s how the parts fit together, in plain English.
The four parts of Medicare
Part A: hospital insurance
Helps cover inpatient hospital stays, care in a skilled nursing facility, hospice care and some home health care.
Part B: medical insurance
Helps cover doctor visits, outpatient care, many preventive services and durable medical equipment.
Parts A and B together are called Original Medicare.
Part C: Medicare Advantage
An alternative way to get your Part A and Part B coverage, through a private insurance company that contracts with Medicare. Learn about Medicare Advantage.
Part D: prescription drug coverage
Helps cover the cost of prescription drugs. It’s offered by private plans that contract with Medicare, either as a stand-alone plan or included in a Medicare Advantage plan. Learn about Part D.
Good to know: “Part C” (Medicare Advantage) is different from “Plan C,” which is one of the lettered Medicare Supplement plans.
Who is eligible?
- People 65 or older
- People under 65 who have received Social Security disability benefits for 24 months
- People with End-Stage Renal Disease (permanent kidney failure needing dialysis or a transplant)
- People with ALS (Lou Gehrig’s disease), as soon as their disability benefits begin
How to sign up
If you already get Social Security benefits, you’ll usually be enrolled in Parts A and B automatically when you turn 65, and your card will arrive in the mail. If not, you can sign up through Social Security at ssa.gov, by phone, or at a local office.
Avoiding late enrollment penalties
If you don’t sign up for Part B when you’re first eligible, and you don’t have other qualifying coverage (such as from a current employer), you may pay a late enrollment penalty for as long as you have Part B. A separate penalty can apply to Part D. See the enrollment periods.
Reviewed October 2026. Medicare rules and costs change every year. For the latest official information, visit Medicare.gov or call 1-800-MEDICARE (TTY 1-877-486-2048).
Medicare, explained
Explore each option
Not sure where to start? Here’s how the main parts of Medicare fit together.
Original Medicare (Parts A & B)
Hospital and medical insurance from the federal government.
Medicare Advantage (Part C)
An alternative to Original Medicare, offered by private companies that contract with Medicare.
Prescription Drug Plans (Part D)
Drug coverage from private plans that contract with Medicare.
Medicare Supplement (Medigap)
Private insurance that helps pay some costs Original Medicare doesn’t, like copays and deductibles.
Questions about Medicare? Talk with a licensed agent.
Mon–Fri, 8 a.m.–6 p.m. ET · TTY: +1 877-486-2048