Medicare has four parts — A, B, C, and D — and the letters alone do not tell you much. If you are approaching 65 or helping a family member get enrolled, this plain-language breakdown covers what each part is, what it does, and why the distinctions matter.
Part A — Hospital Coverage
Part A covers inpatient hospital stays, skilled nursing facility care (after a qualifying hospital stay), hospice care, and some home health care.
Most people do not pay a monthly premium for Part A if they or their spouse worked and paid Medicare taxes for at least ten years. It is generally the first part of Medicare to kick in.
Part B — Medical Coverage
Part B covers outpatient care: doctor visits, lab tests, preventive screenings, outpatient surgery, durable medical equipment, and some home health services. Think of it as the coverage for care you receive outside of a hospital.
Part B does have a monthly premium, and the amount can vary based on your income. There is also an annual deductible before Part B begins paying. Most people enroll in Part B when they first become eligible, unless they have qualifying employer coverage.
Parts A and B Together: Original Medicare
Parts A and B together make up what is called Original Medicare — the traditional federal program administered directly by the government. If you have Original Medicare, you can see any doctor or specialist in the country who accepts Medicare, with no referrals required.
Original Medicare does not cover everything. It has deductibles, coinsurance, and coverage gaps — which is why many people add either a Medigap supplement plan (see below) or choose Part C instead.
Part C — Medicare Advantage
Part C, also called Medicare Advantage, is an alternative way to receive your Medicare benefits through a private insurance company approved by Medicare.
Medicare Advantage plans often bundle Parts A, B, and D into a single plan and may include additional benefits. However, they typically require you to use a specific network of doctors and get referrals for specialists. Costs and coverage vary significantly by plan and location.
Choosing between Original Medicare and Medicare Advantage is one of the most important enrollment decisions you will make. Both paths have trade-offs — neither is universally better.
Part D — Prescription Drug Coverage
Part D covers prescription drugs. It is offered through private insurance companies approved by Medicare and is separate from Parts A and B.
If you are enrolled in Original Medicare, you add Part D coverage separately by choosing a standalone drug plan. If you choose Medicare Advantage, drug coverage is usually included in the plan.
There is a late enrollment penalty for Part D if you go without creditable drug coverage for an extended period after you first become eligible — so it is important not to skip it unless you have qualifying coverage elsewhere.
Medigap — Supplemental Coverage for Original Medicare
Medigap (Medicare Supplement Insurance) is not one of the four parts, but it is worth understanding. These are private insurance policies that pay some or all of the out-of-pocket costs that Original Medicare does not cover — deductibles, coinsurance, and copayments.
If you choose Original Medicare, adding a Medigap plan can provide significant cost predictability. Medigap plans are standardized by letter (Plan G, Plan N, etc.) so you can compare them by price rather than by benefits.
You cannot use a Medigap plan with Medicare Advantage — it is one or the other.
Where to Learn More
- Medicare.gov — medicare.gov The official federal site for Medicare — plan finder, coverage information, and enrollment tools.
- State Health Insurance Assistance Program (SHIP) — shiphelp.org Free, unbiased Medicare counseling from trained volunteers in every state. No sales pitch.
- Medicare Interactive — medicareinteractive.org A plain-language resource from the Medicare Rights Center covering enrollment, coverage rules, and your rights.