Medigap Plans: Complete Guide to Medicare Supplement Insurance

Medicare supplement plans (also known as Medigap plans) are supplements in which insurance companies offer coverage to cover the gaps in Original Medicare. Original Medicare is available to cover approximately 80 percent of Part B expenses provided you pay the annual deductible leaving you with the remaining 20 percent of the Part B costs. A Medigap policy limits that exposure. KFF research indicates that about 12 million Medicare beneficiaries now have Medigap coverage.

This guide describes what Medigap insurance is, the standardized plan letters that will be offered in 2026, what each covers, what they cost and how to compare Medigap vs Medicare Advantage. The sources of information are Medicare.gov, CMS, NAIC, and KFF. 

What is Medigap?

What is Medigap? It is a Medicare supplement insurance plan offered by individual insurers that covers your portion of the costs when Medicare covers its portion of the costs. Medigap does not take the place of Medicare. It acts in concert with it. Your premiums in Part B remain unchanged (in 2026, Part B would be a $185.00 premium). and the Medigap policy will cover most or all of the deductibles, coinsurgery, and copays that otherwise would come out of your pocket. 

A few key facts about Medigap insurance:

• Plans are standardized by federal law. A Plan G from one insurer covers exactly the same things as a Plan G from another insurer. Premium prices vary, coverage doesn't.

• You can use any provider that accepts Medicare. No networks, no referrals, no prior authorization for most services.

• Medigap doesn't cover prescriptions. You need a separate Medicare Part D plan for that.

• You can't have Medigap and Medicare Advantage at the same time. They're alternative paths to coverage.

Standardization is what makes Medigap different from most insurance. Federal law (and three additional plan structures in Wisconsin, Massachusetts, and Minnesota) requires every Medigap plan to follow the same coverage chart. The only differences between insurers selling the same plan letter are the premium and customer service.

Medicare supplement plans: the standardized plan letters

Medicare supplement plans are identified by letters: A, B, C, D, F, G, K, L, M, and N. Each letter has a fixed coverage profile. Two letters (Plans C and F) are no longer available to people newly eligible for Medicare on or after January 1, 2020, due to MACRA reform.

The plans available to most new beneficiaries in 2026 are A, B, D, G, K, L, M, and N. The two most popular are Plan G and Plan N. Together they account for the vast majority of new Medigap enrollments.

Plans K and L cap your annual out-of-pocket spending. Plans G and N are the most popular among new enrollees because they balance coverage and premium.

Best Medigap plans for most people

There's no universal "best" Medigap plan. The right choice depends on how often you use healthcare, how much premium you can afford, and whether you value first-dollar coverage or are willing to pay small copays for lower monthly costs.

For most new beneficiaries, the choice comes down to two:

Plan G covers everything Original Medicare doesn't, except the $257 annual Part B deductible. After you pay the deductible, your covered care for the rest of the year is at zero out-of-pocket cost. Typical 2026 premium: $150 to $300 per month at age 65.

Plan N covers most of the same gaps but charges small copays at the time of service ($20 for office visits, up to $50 for ER visits that don't result in admission). Typical 2026 premium: $100 to $200 per month, often $30 to $80 less than Plan G.

For people who were eligible before January 1, 2020, Plan F is also worth considering. Plan F covers the Part B deductible too, but its higher premium often exceeds the $257 deductible savings.

Medigap plan comparison: Plan G vs Plan N

Plan G vs Plan N is the most common comparison new Medicare beneficiaries face. Both plans cover essentially the same things, with two differences.

If you visit doctors infrequently, Plan N's lower premium can save hundreds annually. If you visit often, the office visit copays add up and Plan G's first-dollar coverage may be a better deal. Most Medicare brokers run premium quotes for both before recommending one. See our dedicated Plan G guide and Plan N guide for deeper comparisons.

Medigap vs Medicare Advantage

Medigap vs Medicare Advantage is the bigger structural choice. Both pair with Original Medicare, but in opposite ways. Medigap supplements Original Medicare. Medicare Advantage replaces it with a private insurer's bundled plan.

If you travel often, see specialists, or value provider flexibility, Medigap with Plan G or Plan N is usually the right choice. If you're healthy, want low monthly costs, and don't mind a network, Medicare Advantage may save money. About 54% of Medicare-eligible adults choose Medicare Advantage in 2026, and 46% choose Original Medicare with or without a Medigap supplement.

When to enroll in Medigap

The Medigap Open Enrollment Period is the most important Medigap rule. It is a 6-month period during which an insurer is required to sell you any Medigap plan available to you, at the best possible rate, and regardless of whether you are healthy or not.

Beyond this window, in most states, insurers can underwrite (review your medical history) and either decline to cover or charge higher premiums based on health conditions. They are the exception; a few states (Connecticut, Maine, Massachusetts, New York) have to offer Medigap all year round without underwriting.

When you fail to have your Open Enrollment Period, you will still be able to receive coverage, but the selection will be very limited. Before losing this window, talk to a Medicare-licensed broker.