Overview: Because Original Medicare leaves beneficiaries exposed to unlimited coinsurance and multiple deductibles, a robust private market of supplemental insurance has developed — and understanding the standardized plan structure is essential exam content.

How Medigap Works

A Medigap policy is private health insurance sold by state-licensed insurance companies to fill cost-sharing gaps in Original Medicare. When you receive a covered service, Medicare pays its share first, and the Medigap policy pays some or all of the remainder. Medigap covers only costs that arise under Original Medicare — it does not add new benefits like dental, vision, or prescription drugs. You cannot have a Medigap policy and a Medicare Advantage plan simultaneously.

In most states, Medigap plans are federally standardized: every plan labeled "Plan G" from any insurer must offer identical benefits. The only difference between the same letter plan from two different insurers is the premium and the insurer's reputation for service.

The Ten Standardized Plans

The 10 available Medigap plans are labeled A, B, C, D, F, G, K, L, M, and N. Plans C and F are grandfathered — they are no longer available to individuals who became eligible for Medicare on or after January 1, 2020, because those plans cover the Part B deductible, which federal law now prohibits for new enrollees.

Core benefits all plans share: Every Medigap plan must cover: (1) Part A coinsurance and hospital costs for up to 365 days beyond Medicare's benefits, (2) Part B coinsurance or copayment, (3) the first three pints of blood, and (4) Part A hospice care coinsurance or copayment.

How the optional benefits differ:

Benefit	Plans Covering It	Notable Exceptions
Part A deductible (100%)	B, C, D, F, G, N	A does not; M covers 50%
Part B deductible	C, F only	Not available to post-2020 enrollees
Part B excess charges	F, G	No other plan covers this
SNF coinsurance (100%)	C, D, F, G, M, N	K covers 50%; L covers 75%; A, B do not cover
Foreign travel emergency (80%)	C, D, F, G, M, N	A, B, K, L do not cover
Out-of-pocket spending limit	K ($8,000), L ($4,000)	Other plans have no annual limit structure

Plan G is currently the most comprehensive plan available to new enrollees — it covers everything Plan F covers except the Part B deductible. A beneficiary on Plan G effectively pays only the $283 annual Part B deductible, and Medigap covers essentially all other Medicare cost-sharing. Plan N is popular for cost-conscious beneficiaries willing to pay small copayments ($20 for office visits, $50 for emergency room visits) in exchange for a lower monthly premium, though it does not cover Part B excess charges.