Original Medicare covers a lot, but it does not cover everything. Deductibles, coinsurance, and copayments can add up quickly if you have significant health needs. Medigap — short for Medicare Supplement Insurance — is a type of private insurance designed to fill those gaps.
What Medigap Does
When you have Original Medicare (Parts A and B) and use a medical service, Medicare pays its share and you pay the rest out of pocket. Medigap is a separate policy that pays some or all of that remaining share, depending on the plan you choose.
Medigap does not replace Medicare — it works alongside it. You keep your Original Medicare coverage, and Medigap picks up costs Medicare leaves behind.
Medigap can help cover:
- Part A hospital deductible and coinsurance
- Part B coinsurance (typically 20% of outpatient costs)
- Skilled nursing facility coinsurance
- Emergency care during foreign travel (on some plans)
Medigap does not cover prescription drugs — for that, you need a separate Part D plan.
How Plans Are Standardized
Medigap plans are standardized by letter. In most states, a Plan G from one insurance company covers exactly the same benefits as a Plan G from any other company — the only difference is the monthly premium you pay.
This makes comparison shopping straightforward: once you decide which plan letter fits your needs, you can shop purely on price. Plans commonly available include Plan G and Plan N, among others. The right choice depends on your health situation and how much premium versus out-of-pocket cost tradeoff works for you.
A SHIP counselor (free, unbiased — see below) can walk you through the plan options in your state without any sales pressure.
The Best Time to Buy: Open Enrollment
The most important thing to know about Medigap is that you have a guaranteed enrollment window when you first sign up for Part B. During the six-month period that begins the month you turn 65 and are enrolled in Part B:
- Insurance companies must sell you any Medigap plan they offer
- They cannot charge you more based on health conditions
- They cannot turn you down
After this window closes, insurance companies in most states can use medical underwriting — meaning they can charge more or deny coverage based on your health history. This makes timing critical.
If you miss this window and have health conditions, getting Medigap later may be difficult or expensive. There are some exceptions (certain qualifying life events), but the best approach is to enroll during your guaranteed window.
Medigap vs. Medicare Advantage
You cannot have both Medigap and Medicare Advantage. They are two different approaches to the same problem:
- Medigap + Original Medicare: You can see any Medicare-accepting doctor nationwide. Costs are more predictable. Monthly premium is higher.
- Medicare Advantage: Coverage bundled through a private plan with a network of providers. Monthly premium is often lower, sometimes zero, but out-of-pocket costs can be higher when you use services.
Switching from Medicare Advantage back to Original Medicare and then trying to buy a Medigap plan later is where many people run into problems — because the guaranteed enrollment window has passed and medical underwriting may apply.
If you are deciding between these paths for the first time, speak with a SHIP counselor before enrolling.
Where to Learn More
- State Health Insurance Assistance Program (SHIP) — shiphelp.org Free, unbiased Medigap and Medicare counseling in every state — the best first call for comparing your options.
- Medicare.gov — Medigap — medicare.gov/supplements-other-insurance/whats-medicare-supplement-insurance-medigap Official federal overview of how Medigap works, what plans are available, and how to shop.
- Medicare Rights Center — medicarerights.org A nonprofit that provides free counseling and consumer guides on Medicare Supplement options and rights.