Medicare Supplement (Medigap) Insurance: What It Covers and When to Buy It

Original Medicare — Parts A and B — covers a lot, but it does not cover everything. You still pay a Part B deductible, 20% of most outpatient services, and significant cost-sharing for hospital stays. For people who see doctors regularly or have chronic health conditions, these out-of-pocket costs can add up to thousands of dollars a year.

Medicare Supplement insurance, commonly called Medigap, is sold by private insurance companies and fills in some or all of those gaps. You pay a monthly premium to the Medigap insurer, and in exchange, they pay all or most of your cost-sharing under original Medicare.

How Medigap works

Medigap plans are standardized by the federal government. In most states, plans are labeled by letters: Plan A, Plan B, Plan C, Plan D, Plan F, Plan G, Plan K, Plan L, Plan M, and Plan N. (Plan F is no longer available to new enrollees who became eligible for Medicare after January 1, 2020.)

Each plan letter covers the same benefits regardless of which insurance company sells it — the only difference between companies is the monthly premium. Plan G is currently the most comprehensive plan available to new enrollees.

What Medigap covers

Most Medigap plans cover: the Part A coinsurance and hospital costs, the Part B coinsurance (20%), blood transfusions, hospice coinsurance, and some cover the Part A and Part B deductibles. Most do NOT cover dental, vision, hearing, or prescription drugs — you still need a separate Part D drug plan.

Medigap vs. Medicare Advantage (Part C)

These are two different ways to supplement Medicare. Medigap works alongside original Medicare — you can see any doctor or hospital in the US that accepts Medicare, which is most of them. Medicare Advantage replaces original Medicare with a private plan that usually has lower premiums but requires you to use a specific network of providers.

The best time to buy Medigap

The best time to buy Medigap is during your Medigap Open Enrollment Period — the 6 months that begin the first month you are both 65 or older and enrolled in Part B. During this window, insurance companies must sell you a policy at the best available rate regardless of your health history. After this window closes, you can be denied or charged higher rates based on pre-existing conditions in most states.

Quick Tip: Compare Medigap premiums in your area at medicare.gov/plan-compare. The same standardized plan can vary by hundreds of dollars per month between insurers — shopping around is worth the time.