What's the difference between Medicare Parts A, B, C, and D?

• Part A — hospital coverage. Most people pay no premium for it.
• Part B — doctor and outpatient coverage. This one has a monthly premium.
• A + B together are called Original Medicare.
• Part C — Medicare Advantage. A private plan that delivers your A and B benefits in one package, usually with drug coverage included.
• Part D — prescription drug coverage, sold by private companies.
• The real decision is Original Medicare or Medicare Advantage — not four checkboxes.

The letters came along one at a time over sixty years, so they don't describe a tidy system. Reading them as A, B, C, D in order makes it look like four equal choices. They are not equal, and two of them are not really choices at all in the way people expect.

A cleaner way to hold it: A and B are the foundation. C and D are what you build on top of it — or instead of part of it.

Part A covers you when you are admitted to a hospital. It also covers skilled nursing facility care after a qualifying hospital stay, hospice care, and some home health care.

Most people pay nothing each month for Part A. If you or your spouse worked and paid Medicare taxes for about ten years, you have earned it, and it is premium-free. That is why most people take Part A when they become eligible, even people who are still working and delaying the rest.

Premium-free does not mean cost-free. Part A has a deductible each benefit period — currently $1,736 — and daily coinsurance kicks in on long stays.

Part B is the part you use in ordinary life: doctor visits, outpatient procedures, lab work, preventive screenings, and durable medical equipment like a walker or oxygen.

Part B has a monthly premium ($202.90 for most people in 2026, higher for higher incomes) and an annual deductible of $283. After the deductible, you generally pay 20% of the approved amount for most services.

That 20% is the detail worth slowing down on. In Original Medicare there is no annual cap on it. Twenty percent of a routine visit is small. Twenty percent of a cancer treatment year is not, and it keeps going. The supplements and Advantage plans are two common answers to that gap.

Part C is not an extra layer on top of A and B. It is a different way of receiving them.

A private insurer approved by Medicare bundles your Part A and Part B benefits into one plan, usually folds in prescription coverage, and often adds things Original Medicare does not include. These plans work through networks, so which doctors you can see matters in a way it generally doesn't under Original Medicare.

They do include something Original Medicare lacks: an annual out-of-pocket maximum. Once you hit it, the plan covers the rest of your covered Part A and B costs for that year. Medicare caps how high that limit can be set — $9,850 in-network for 2027 — and plans may set theirs lower.

One thing people are routinely surprised by: you keep paying your Part B premium when you are on a Medicare Advantage plan. You have not left Medicare. You are receiving it through a private company instead of directly.

Original Medicare does not cover most prescriptions you pick up at a pharmacy. Part D is the fix, and it is sold by private companies rather than by Medicare itself.

You can get it two ways: as a standalone drug plan alongside Original Medicare, or built into a Medicare Advantage plan. Every Part D plan has a formulary — its own list of covered drugs — and those lists differ from plan to plan. Two people on the same medication can have very different experiences depending on which plan they chose.

If you skip Part D when you first become eligible and don't have other drug coverage that counts, a late penalty can attach to your premium permanently. It is one of the more avoidable expensive mistakes in Medicare.