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Medicare Basics: Parts A, B, C, and D Explained

Medicare's alphabet of parts trips up a lot of people right before they need it most. Here's what each part actually covers.

Part A: hospital insurance

Part A covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health care. Most people do not pay a monthly premium for Part A if they or a spouse paid Medicare payroll taxes for enough working years.

Part B: medical insurance

Part B covers outpatient care: doctor visits, preventive services, durable medical equipment, and outpatient procedures. Unlike Part A, almost everyone pays a monthly premium for Part B, and the amount can be higher for people with higher income, an income-related surcharge known as IRMAA.

Part C: Medicare Advantage

Medicare Advantage plans are an alternative way to get Medicare benefits, sold by private insurers approved by Medicare. They bundle Parts A and B, and usually Part D, into one plan, often with extra benefits like dental or vision, but typically restrict you to a network of providers.

Part D: prescription drug coverage

Part D covers outpatient prescription drugs through private, Medicare-approved insurers. It is optional, but going without it or without other creditable drug coverage once you are eligible can trigger a permanent late-enrollment penalty added to your premium.

Eligibility mostly starts at 65

Most people become eligible for Medicare at age 65, regardless of whether they have retired. People under 65 can also qualify earlier due to certain disabilities or specific conditions like end-stage renal disease.

The Initial Enrollment Period is a 7-month window

This window is centered on your 65th birthday month: it starts 3 months before, includes the birthday month, and extends 3 months after. Enrolling late without other qualifying coverage can mean a delay in coverage and a permanent premium penalty.

Medigap fills gaps in Original Medicare

Medigap, or Medicare Supplement, policies are separate private plans that help cover the deductibles, copays, and coinsurance that Original Medicare (Parts A and B) leaves you to pay. Medigap and Medicare Advantage are not used together β€” they are two different approaches to filling the same gaps.

Annual Open Enrollment lets you change plans each fall

Every year, a window in the fall lets people already on Medicare switch Advantage plans, switch drug plans, or move between Original Medicare and Medicare Advantage for the coming year.

Why the parts are lettered instead of named

Medicare was created in 1965 covering hospital and medical insurance, which became Parts A and B. Part C (Medicare Advantage) and Part D (drug coverage) were added decades later as the program expanded, which is why the letters do not map neatly onto 'basic' vs 'extra' coverage the way a newcomer might expect.

Original Medicare vs Medicare Advantage is the real fork in the road

The biggest practical decision most new enrollees face is not which letter to pick but whether to stay on Original Medicare, Parts A and B, optionally paired with a Medigap policy and a standalone Part D plan, or switch to a Medicare Advantage plan. Each path has different trade-offs around provider networks, extra benefits, and out-of-pocket cost predictability.

The late-enrollment penalties are permanent, not one-time

Delaying Part B or Part D enrollment without another form of qualifying coverage does not just cost you a one-time late fee β€” it typically adds a permanent percentage increase to your premium for as long as you have that coverage, which is why understanding your enrollment window matters even years before you turn 65.

Frequently Asked Questions

Do I need to sign up for Medicare if I am still working at 65?

It depends on the size of your employer and your current coverage. Many people with qualifying employer coverage can delay Part B without a penalty, but the rules are specific enough that it is worth confirming your situation directly with Medicare or your employer's benefits office before your Initial Enrollment Period ends.

Is Medicare free?

No single part of Medicare is entirely free for most people. Part A usually has no premium if you have enough work history, but Part B, Part D, and any supplemental coverage generally carry a monthly premium, plus deductibles and coinsurance depending on the services you use.

What is the difference between Medicare and Medicaid?

They are separate programs despite the similar names. Medicare is a federal program primarily based on age or disability, regardless of income, while Medicaid is a joint federal-state program based primarily on income and, in some cases, other eligibility factors, with rules that vary by state.

Can I have both Medicare and employer or marketplace insurance?

In some cases yes, but coordination-of-benefits rules determine which plan pays first, and the details depend on the type of other coverage and your specific situation, so it is worth checking rather than assuming.