Parts A, B, C, and D: what each actually covers

Medicare’s four parts are often mentioned by letter without much explanation, which makes the system harder to navigate than it needs to be. Each part covers something different, and most people end up combining several of them.

Part A: hospital insurance

Part A covers inpatient hospital stays, skilled nursing facility care (after a qualifying hospital stay), hospice care, and some home health care. Most people don’t pay a monthly premium for Part A if they or a spouse paid Medicare taxes for at least 10 years of work — which is why it’s often described as “free,” though deductibles and coinsurance still apply when care is actually used.

Part B: medical insurance

Part B covers outpatient care: doctor visits, preventive services, durable medical equipment, and outpatient procedures. Unlike Part A, Part B carries a monthly premium for everyone, which increases at higher income levels (a surcharge called IRMAA, covered in more detail in IRMAA: when Medicare costs more because of your income). Part B is also where the enrollment timing rules matter most — late enrollment carries a permanent premium penalty, covered in Medicare enrollment: what the timeline actually looks like.

Part C: Medicare Advantage

Part C, branded as Medicare Advantage, is an alternative way to receive Part A and B benefits through a private insurer, usually bundled with Part D drug coverage and often additional benefits (vision, dental, hearing) that Original Medicare doesn’t include. The trade-off is usually network restrictions — Medicare Advantage plans typically use HMO or PPO networks, unlike Original Medicare’s broader provider access. Medigap vs. Medicare Advantage: how to choose covers this trade-off in more depth.

Part D: prescription drug coverage

Part D covers prescription medications, offered through private insurers with varying drug formularies (the list of covered medications) and costs. Like Part B, Part D has its own late-enrollment penalty for those who go without coverage for an extended period without an exception — worth checking even for someone who currently takes no medications, since enrolling later, after a need arises, can mean paying a permanent penalty.

How these typically combine

Most people end up choosing between two overall paths: Original Medicare (Parts A and B) supplemented by a Medigap policy and a standalone Part D plan, or a Medicare Advantage plan (Part C) that bundles everything together. Neither path is universally better — it depends on provider preferences, travel patterns, and specific health needs. The Medicare.gov coverage finder lets you check whether a specific service or item is covered under a given path.

Related reading: Medicare enrollment: what the timeline actually looks like and Medigap vs. Medicare Advantage: how to choose.