Medigap explained: what it covers and why timing matters

What Medigap does

Medigap, also called Medicare Supplement Insurance, is a private policy that helps pay some of the costs Original Medicare (Parts A and B) leaves you with, like coinsurance, copayments and deductibles. You must have Part A and Part B to buy it. You pay a monthly premium to the insurance company, on top of your Part B premium.

Medigap works only with Original Medicare. It doesn't work with Medicare Advantage Plans, and it can't be used to pay Medicare Advantage costs. It also doesn't include drug coverage, so most people with Medigap also join a separate Part D drug plan.

The plans are standardized

In most states, Medigap policies are standardized and named by letter: Plans A, B, C, D, F, G, K, L, M and N. A Plan G from one company has the same basic benefits as a Plan G from any other company; the main differences are price and customer service. That makes it easier to shop: decide which letter you want, then compare prices. Massachusetts, Minnesota and Wisconsin standardize their policies differently.

Plans C and F, which cover the Part B deductible, aren't available to people who became eligible for Medicare on or after January 1, 2020. If you were eligible before then, you may still be able to buy them.

Your Medigap Open Enrollment Period

The best time to buy Medigap is during your six-month Medigap Open Enrollment Period. It starts the first month you have Part B and are 65 or older. During this window, a company can't refuse to sell you any policy it offers, and it can't charge you more because of health problems.

After this window ends, in most states insurers can use medical underwriting: they can ask about your health and charge more or turn you down. That's why switching from Medicare Advantage to Original Medicare later can make Medigap hard or costly to get. Some states give extra protections, and there are some federal "guaranteed issue" situations, such as when a Medicare Advantage Plan leaves your area.

How prices are set

Companies price Medigap in one of three ways: community-rated (everyone pays the same, regardless of age), issue-age-rated (based on your age when you buy) or attained-age-rated (premiums rise as you get older). Ask which method a company uses, because a policy that's cheap at 65 can get expensive later.

Medigap or Medicare Advantage?

Original Medicare plus Medigap usually costs more each month but lets you see any doctor or hospital in the U.S. that accepts Medicare, with predictable out-of-pocket costs. Medicare Advantage Plans often have low or $0 premiums but use networks, prior authorization and copays. There's no single right answer; it depends on your health, budget and where you want to get care. A SHIP counselor can walk you through the trade-offs for free.