What Is Medigap Insurance?
Original Medicare covers a great deal, but it isn’t designed to cover everything, and the deductibles, coinsurance, and copayments left behind can add up. Medigap insurance exists specifically to soften that remaining exposure.
The short answer
Medigap, also called Medicare Supplement Insurance, is a type of private policy that helps pay for some of the out-of-pocket costs Original Medicare doesn’t cover, such as deductibles, coinsurance, and copayments. It’s sold by private insurers but works only alongside Original Medicare’s Part A and Part B, not alongside Medicare Advantage. The plans are standardized into lettered categories, so a plan with a given letter offers the same core benefits no matter which insurer sells it, though the premium charged for that letter can vary by company.
Why the lettered plans matter
Unlike many types of insurance, where every insurer designs its own policy from scratch, Medigap plans are standardized by letter (Plan G and Plan N are common examples), and the specific benefits attached to each letter are set by the government rather than by the individual insurance company. That means comparing a Plan G from one insurer to a Plan G from another is mostly a comparison of price and customer service, not a comparison of what’s actually covered, since the coverage itself is the same by design. This standardization is meant to make comparison shopping simpler than it would be if every insurer’s policy covered a different mix of gaps.
Why it doesn’t pair with Medicare Advantage
Medigap is built specifically to supplement Original Medicare’s cost-sharing structure, filling in the deductibles and coinsurance that Part A and Part B leave behind. Medicare Advantage restructures the benefit entirely through a private insurer with its own network and cost-sharing rules, so there’s no equivalent gap for a Medigap policy to fill, and holding both at the same time generally isn’t allowed. This is one of the clearer either-or points in the Medicare system: choosing Original Medicare with a possible Medigap policy, or choosing Medicare Advantage instead, rather than combining the two.
What Medigap typically doesn’t cover
Even though Medigap fills many of Original Medicare’s gaps, it isn’t comprehensive. Most Medigap plans don’t include prescription drug coverage, which is why people often pair a Medigap policy with a separate Part D plan for prescriptions. Medigap also generally doesn’t cover services that Original Medicare doesn’t cover at all, such as most dental, vision, or hearing care, since a supplement can only fill gaps within the coverage it’s built around, not add entirely new categories of benefit.
What to weigh
Choosing whether to add a Medigap policy, and which lettered plan to choose, generally comes down to weighing the added monthly premium against how much unpredictable out-of-pocket cost-sharing someone is comfortable carrying on their own. Because premiums vary by insurer, by region, and by age at enrollment, and because they’re set by individual companies rather than the government, comparing quotes from more than one insurer for the same lettered plan is typically the most useful step before deciding.