The Four Parts of Medicare, Explained in Plain Language

The short answer: Medicare has four parts. Part A covers hospital stays, Part B covers doctors and outpatient care, and together they make up Original Medicare. Part D adds prescription drug coverage. Part C — better known as Medicare Advantage — is a different way of receiving those same benefits through a private plan. Most decisions people wrestle with come down to how these four pieces fit together, and that is what this guide walks through.

Medicare’s alphabet is the first wall people hit. The letters were added over decades, they are not in any logical order of importance, and two of them are not even separate coverage — they are alternate delivery methods. Once you see what each part actually does, the rest of the decisions get much easier to think about.

What does Medicare Part A cover?

Part A is hospital insurance. It covers inpatient hospital stays, care in a skilled nursing facility after a qualifying hospital stay, hospice care, and some home health care.

Most people pay no monthly premium for Part A, because they already paid for it through payroll taxes during their working years. That is why the common advice is to take Part A at 65 even if you are still working — for most people it costs nothing to have. (One important exception: if you are contributing to a Health Savings Account, starting any part of Medicare ends your ability to contribute. Our Medicare timing guide covers that trap in detail.)

Part A is not unlimited, though. It has a deductible per benefit period — not per year, which surprises people — and hospital stays beyond certain lengths carry daily costs. Those gaps are part of what supplemental coverage is designed to handle.

What does Medicare Part B cover?

Part B is medical insurance — the everyday side of health care. Doctor visits, outpatient procedures, lab work, X-rays and imaging, preventive services, durable medical equipment like walkers and oxygen, and most care that happens outside a hospital bed.

Part B carries a monthly premium for everyone, and higher-income households pay more. It also has an annual deductible, and after that Medicare pays 80% of the approved amount for covered services. That remaining 20% is the number to sit with for a moment: it has no annual cap under Original Medicare alone. A serious year of treatment means 20% of a very large number. This single fact is why Medigap plans and Medicare Advantage plans exist, and why going through Medicare with Parts A and B alone is rarely the plan.

Part B is also where the permanent late-enrollment penalty lives — 10% added to the premium for each full 12-month period you could have had it and did not, for as long as you have Part B. The enrollment windows that prevent that are laid out in the timing guide.

What is Medicare Part C (Medicare Advantage)?

Part C is not extra coverage on top of Medicare — it is a different way of receiving Parts A and B. When you join a Medicare Advantage plan, a private insurance company takes over delivering your Medicare benefits, usually bundling drug coverage in, and often adding extras like dental or vision allowances.

In exchange, you generally agree to use the plan’s network of doctors and hospitals and follow its rules, such as getting referrals or prior authorizations for certain care. Costs work differently too: instead of Medicare’s 80/20 split, you pay the plan’s copays as you go, with an annual out-of-pocket maximum as a backstop.

Medicare Advantage is neither a trap nor a miracle — it is a genuinely different structure with real trade-offs in both directions. We compare the two paths honestly in Medigap vs. Medicare Advantage.

What does Medicare Part D cover?

Part D is prescription drug coverage, sold by private companies either as a standalone plan (alongside Original Medicare) or built into a Medicare Advantage plan.

Every Part D plan has a formulary — its list of covered drugs, sorted into tiers that determine what you pay. Two plans with similar premiums can treat the same prescription very differently, which is why the right Part D plan is a personal calculation, not a popularity contest. Since 2025, annual out-of-pocket drug costs under Part D are capped, which removed the old “donut hole” fear from the equation — a genuine improvement.

Part D has its own permanent late penalty: go 63 days or more without drug coverage that counts as creditable, and a penalty attaches for every month you waited. It applies even if you take no medications today. If you are healthy at 65, the cheapest suitable plan usually beats no plan.

How do the parts fit together?

Nearly everyone on Medicare ends up in one of two configurations:

• Original Medicare + supplement + drug plan. Parts A and B from Medicare, a Medigap plan to cover the gaps (like that uncapped 20%), and a standalone Part D plan for prescriptions. Any doctor in the country who accepts Medicare, at predictable cost.
• Medicare Advantage. Parts A, B, and usually D delivered together through one private plan, typically with a lower monthly cost, a network, and pay-as-you-go copays.

Neither is right for everyone. Health, budget, travel habits, and the doctors you already trust all pull the decision in different directions — and the choice you make at 65 affects which options stay open later, because supplement plans can require health underwriting after your first enrollment window closes.

Common questions about the parts of Medicare

Do I need all four parts of Medicare?

Almost everyone takes Part A. Part B is essential unless you have qualifying employer coverage. Drug coverage — through Part D or a Medicare Advantage plan — is strongly recommended even for people on no medications, because of the permanent late penalty. Part C is optional by definition: it is one of two ways to structure everything else, not an additional layer.

What is the difference between Part C and a Medicare Supplement?

Part C (Medicare Advantage) replaces how you receive Parts A and B — a private plan delivers your benefits, usually with a network. A Medicare Supplement (Medigap) works alongside Original Medicare, paying the deductibles and the 20% that Medicare leaves behind. You can have one or the other, never both at once.

Does Medicare cover dental, vision, or hearing?

Original Medicare generally does not cover routine dental care, eye exams for glasses, or hearing aids. Some Medicare Advantage plans include allowances for these, and standalone dental and vision policies exist for people on Original Medicare. It is a real gap worth planning for either way.

Does Medicare Part A really have no monthly premium?

For most people, yes — no monthly premium, because you prepaid through payroll taxes over your working life. You still have cost-sharing when you use it, like the per-benefit-period deductible. People with shorter work histories may pay a monthly premium for Part A, though that situation is less common.

The simple version

A is the hospital. B is the doctor. D is the pharmacy. C is a different way of packaging all of it through a private plan. Start with the Medicare basics page to see how this fits your own timeline, and the Turning-65 Checklist if your birthday is on the horizon. Georgia residents should also read what is different about turning 65 in Georgia.

Questions about your own situation? Call or text 770-765-7007 — plain-language answers at no cost, from someone who’s still there after you enroll. We’re based in Cumming, Georgia, working with families across North Georgia — and licensed in states across the country, so wherever you’re reading from, the conversation works the same.