Medicare Parts A, B, C, D Explained in Plain English

Medicare gets confusing fast, mostly because it's really four separate pieces that get talked about like one thing. Once you see how each letter fits, the rest of the decisions get a lot easier. Here's the plain-English version.

Part A — hospital coverage

Part A generally covers inpatient hospital stays, care in a skilled nursing facility, some home health care, and hospice care. Most people don't pay a monthly premium for Part A because it's earned through years of work history — for most, it's the part of Medicare that shows up "already paid for."

Part B — medical coverage

Part B covers outpatient care: doctor visits, preventive services, durable medical equipment, and other medical services that don't require a hospital stay. Unlike Part A, Part B carries an ongoing monthly premium for nearly everyone. Together, Part A and Part B are what people mean by "Original Medicare."

Part C — Medicare Advantage

Part C is an alternative way to receive your Medicare benefits, through private insurance companies approved by Medicare. A Medicare Advantage plan generally bundles Part A and Part B coverage together, and usually includes prescription drug coverage as well. Each plan sets its own network of doctors and hospitals, so this is where the "which doctors are in-network" question starts to matter a lot.

Part D — prescription drug coverage

Part D covers prescription medications. It's available either as a standalone drug plan (paired with Original Medicare) or built into a Medicare Advantage plan. Every Part D plan — standalone or bundled — maintains its own formulary: a list of covered medications and the rules around them, including which tier a drug falls into and whether it requires prior authorization.

How the pieces fit together

In practice, most people end up choosing between two structures:

• Original Medicare (Part A + Part B), often paired with a standalone Part D plan and sometimes a supplemental (Medigap) policy to help with the costs Original Medicare doesn't cover.
• Medicare Advantage (Part C), which typically rolls Part A, Part B, and Part D coverage into one plan through a private insurer.

Generally, you don't combine a Medicare Advantage plan with a standalone Part D plan or a Medigap policy — the structures are built to work one way or the other, not mixed. We cover how to think through that choice in a separate post.

Why the letters matter less than the details

Knowing what A, B, C, and D stand for is a good start, but the letters alone won't tell you whether your doctors are in a plan's network or whether your medications are covered the way you'd expect. That's a conversation that has to happen at the plan level, using your actual doctors and prescriptions — not a general description of what the letter covers.