The plain-English guide to Medicare.

If you are turning 65 or helping a parent who is, the first step is understanding the basic building blocks. Medicare is not one product. It is a federal program with four parts that you can mix and match in two main ways.

The four parts of Medicare

Part A — Hospital Insurance

Covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health care. For most people, Part A is free because you (or your spouse) paid Medicare taxes while working. There is a deductible per benefit period and coinsurance for long stays.

Part B — Medical Insurance

Covers doctor visits, outpatient care, preventive services, lab work, and durable medical equipment. Part B has a monthly premium ($174.70 standard for 2026) and a small annual deductible. Higher earners pay an additional premium called IRMAA based on their tax return from two years prior.

Part C — Medicare Advantage

A private alternative to Original Medicare. A single Medicare Advantage plan bundles Parts A, B, and usually D, and often adds dental, vision, hearing, fitness, and an over-the-counter allowance. You still pay your Part B premium and the plan may have an additional premium (often $0). Trade-off: provider networks and prior authorizations.

Part D — Prescription Drug Coverage

A standalone drug plan you add on top of Original Medicare and Medigap. (Most Medicare Advantage plans already include Part D.) Plans differ widely on which drugs are covered, what tier they are on, and which pharmacies are preferred. The right Part D plan depends almost entirely on the specific medications you take.

The two main paths

Once you have Parts A and B, you choose one of two paths:

Path 1 — Original Medicare + Medigap + Part D

You stay on Original Medicare (Parts A and B) and add a Medicare Supplement (Medigap) policy that pays most or all of your share of costs. You also add a standalone Part D drug plan. This path has higher monthly premiums but very predictable out-of-pocket costs and no networks. You can see any doctor in the country who accepts Medicare.

Path 2 — Medicare Advantage (Part C)

You replace Parts A and B (administratively) with a single private plan that often costs $0 in premium beyond Part B and includes drug coverage and extras. The trade-off is that you use the plan's network of doctors and hospitals, and some services require prior authorization. Out-of-pocket costs vary with use, capped by an annual maximum.

Medicare Advantage vs. Medigap — side by side

Enrollment periods — when to sign up

Miss the wrong window and you could pay a permanent late penalty on Part B or Part D, every month, for the rest of your life. Here are the windows that matter most:

Initial Enrollment Period (IEP)

7 months around your 65th birthday — the 3 months before, the month of, and the 3 months after. This is your first and best window. Coverage starts the month you are eligible if you enroll on time.

Annual Election Period (AEP)

October 15 to December 7 each year. This is when anyone on Medicare can switch Medicare Advantage plans or change Part D plans for the following year. Plans change every year — premiums, formularies, networks — so an annual review matters.

Medicare Advantage Open Enrollment

January 1 to March 31. If you are already on Medicare Advantage, you get one chance early in the year to switch to a different MA plan or move back to Original Medicare.

Special Enrollment Periods (SEP)

Life events — losing employer coverage, moving out of your plan's service area, qualifying for Extra Help — can trigger a 60-day window to enroll or change plans. If something has changed, ask. You may have a window you didn't know about.

General Enrollment Period

If you missed your IEP and don't qualify for an SEP, you can enroll January 1 to March 31 with coverage starting July 1, often with a late penalty.

Common terms you will hear

• Medigap (Medicare Supplement) — a private insurance policy that pays your share of Original Medicare costs. Standardized plans (Plan G, Plan N, etc.) are identical across carriers, only the price differs.
• Formulary — the list of drugs covered by a Part D plan, broken into tiers from cheap generics to expensive specialty drugs.
• MOOP (Maximum Out-of-Pocket) — the most you can pay in a year on a Medicare Advantage plan for in-network covered services.
• IRMAA — the income-related extra premium for Parts B and D if your income from two years ago was above a threshold.
• SNF — Skilled Nursing Facility, which Part A covers after a qualifying hospital stay (not long-term custodial care).
• Donut Hole / Coverage Gap — historically the middle stage of Part D where you paid more out of pocket. The Inflation Reduction Act has changed this — by 2026, Part D out-of-pocket is capped at $2,000 per year.