Parts of Medicare Explained – A, B, C, D and Medigap

What Are the Parts of Medicare?

Direct answer: Medicare consists of four parts — Part A (hospital), Part B (medical), Part C (Medicare Advantage, a private-plan alternative), and Part D (prescription drugs) — plus Medigap, a separate supplemental option that isn’t technically a “part” of Medicare but fills gaps Original Medicare leaves open. Understanding how these pieces fit together, and which combination actually applies to your situation, is the foundation everything else builds on.

What Is Medicare Part A?

Part A is your hospital insurance — covering inpatient care, skilled nursing facility care, hospice services, and limited home health care. Most people with sufficient work history (roughly 40 quarters, about a decade) pay no monthly premium; without that history, you can still enroll, but a premium applies. Part A doesn’t cover everything, which is exactly why many people add supplemental coverage. For the full breakdown — including two details that trip people up, observation status and the skilled nursing eligibility prerequisite — see our complete guide to what Medicare Part A covers.

What Is Medicare Part B?

Part B covers outpatient medical services — doctor visits, diagnostic tests, preventive care, and medical supplies. Together, Parts A and B make up Original Medicare. For the complete picture, including a recent expansion of covered mental health providers worth knowing about, see our full guide to Medicare Part B.

What Is Medicare Part C?

Medicare Advantage (Part C) is a private alternative that replaces Original Medicare entirely, bundling Part A and Part B — often with Part D and extras like dental, vision, and hearing — into one plan. You’ll still pay your standard Part B premium regardless of which plan you choose, plus any plan-specific costs, and most plans require using an in-network provider. For the full picture, including network types and how to actually evaluate a plan, see our complete guide to Medicare Advantage.

What Is Medicare Part D?

Part D is optional prescription drug coverage through private insurers, available as a standalone plan or bundled into Medicare Advantage. Costs depend on your plan’s formulary and your specific drugs’ tier placement, and missing your enrollment window without other creditable coverage risks a permanent penalty. One thing worth knowing upfront: paying a Part D premium doesn’t mean your medications are free — copays or coinsurance still apply per prescription based on tier. For the full picture, including Part D’s recent structural redesign, see our complete guide to Medicare Part D.

What Is Medigap?

Medigap (Medicare Supplement) isn’t officially one of Medicare’s four parts, but it’s essential to understand alongside them. Sold by private insurers, Medigap works alongside Original Medicare to cover many of the copayments, coinsurance, and deductibles Parts A and B leave behind. In exchange for a higher, steadier premium, you get freedom to see any Medicare-accepting provider nationwide, with none of the network restrictions that come with Medicare Advantage. For the full picture, see our complete guide to Medicare Supplements.

Which Parts of Medicare Do I Actually Need?

Original Medicare (Part A and Part B) is the foundation everyone starts with. From there, you’ll generally add Part D for prescription coverage, since neither Part A nor Part B covers most medications. For more complete protection against Original Medicare’s biggest gap — no annual out-of-pocket maximum — you’ll choose between two paths: adding a Medigap policy for maximum flexibility, or switching to Medicare Advantage for bundled benefits and a built-in cost cap. For a deeper walkthrough of that specific decision, see our Medicare Advantage vs. Medigap decision guide.

Bottom Line

Medicare’s “alphabet soup” is more manageable once you see how the pieces actually connect: Parts A and B form the foundation, Part D fills the prescription gap, and Part C or Medigap each solve Original Medicare’s biggest weakness — no cost cap — in different ways with different trade-offs. Assessing your health needs, budget, and provider preferences is what determines the right combination for you specifically, not a one-size-fits-all default. Reach out for personalized guidance to walk through your specific situation with confidence.

Key Takeaways

• Medicare has four parts: A (hospital), B (medical), C (Medicare Advantage, private alternative), and D (prescription drugs) — plus Medigap, a separate supplemental option.
• Parts A and B together form Original Medicare, the foundation most people start with.
• Part D fills the prescription drug gap that neither Part A nor Part B covers.
• Original Medicare alone has no annual out-of-pocket maximum — Medigap and Medicare Advantage each address this differently.
• Medigap offers nationwide, network-free flexibility at a higher premium; Medicare Advantage offers bundled benefits and a cost cap with network restrictions.
• The right combination depends on your specific health needs, budget, and provider preferences — there’s no universal default.

FAQ

What are the four parts of Medicare?
Part A (hospital insurance), Part B (medical insurance), Part C (Medicare Advantage), and Part D (prescription drug coverage).

Is Medigap one of the four parts of Medicare?
No. It’s a separate, private supplemental option that works alongside Original Medicare, not an official “part” of Medicare itself.

Do I need all four parts of Medicare?
Not necessarily. Most people start with Parts A and B, add Part D for prescriptions, and then choose either Medigap or Medicare Advantage — not both — to fill Original Medicare’s remaining gaps.

What’s the biggest gap Original Medicare leaves open?
No annual out-of-pocket maximum — a serious illness can generate open-ended costs, which is why most people add Medigap or Medicare Advantage.

Can I have both Medigap and Medicare Advantage?
No. They’re mutually exclusive — Medigap supplements Original Medicare, while Medicare Advantage replaces it entirely.