Medigap vs. Medicare Advantage Explained

After enrolling in Original Medicare (Parts A and B), most people face gaps in coverage — deductibles, copays, and coinsurance that can add up to thousands of dollars in a single year. Two distinct pathways exist for addressing those gaps: Medicare Supplement insurance, commonly called Medigap, and Medicare Advantage (Part C). These are not add-ons to each other — they represent fundamentally different ways of receiving and financing Medicare benefits. This page describes how each works, what it covers, and the key trade-offs involved. It is not personalized advice; individual circumstances vary significantly.

How Original Medicare leaves gaps

Original Medicare covers a wide range of services but does not cover 100 percent of approved costs. Part A carries a per-benefit-period inpatient deductible and daily coinsurance for extended hospital stays. Part B generally covers 80 percent of approved amounts after a deductible, leaving a 20 percent coinsurance with no annual cap. For someone with a serious illness or a long hospital stay, that uncapped 20 percent can become a major financial exposure.

Neither Original Medicare Part A nor Part B covers routine dental, vision, or hearing services, and neither covers most prescription drugs. Understanding these gaps is the starting point for evaluating supplemental options.

What Medigap is and how it works

Medigap policies are sold by private insurers but are regulated by CMS and state insurance departments. Each plan must meet a standardized benefit structure defined by federal rules, identified by letters A through N (not all plans are available in all states; Massachusetts, Minnesota, and Wisconsin have their own standardization systems).

A Medigap policy works alongside Original Medicare. When you receive a covered service, Medicare pays its share first; the Medigap policy then pays some or all of the remaining cost-sharing, depending on the plan type. You continue to use Original Medicare’s nationwide provider network — any provider that accepts Medicare accepts your Medigap policy, because the policy simply covers the gaps in what Medicare pays.

Common Medigap plans and what they typically cover:

Plan	Part A coinsurance	Part B coinsurance	Part A deductible	Part B deductible	Skilled nursing coinsurance
Plan A	Yes	Yes	No	No	No
Plan G	Yes	Yes	Yes	No	Yes
Plan N	Yes	Yes (with some copays)	Yes	No	Yes
Plan K	50%	50%	50%	No	50%

Plan F (covering all gaps including the Part B deductible) is no longer available to beneficiaries who became Medicare-eligible on or after January 1, 2020.

Medigap policies do not include prescription drug coverage. Beneficiaries who choose Original Medicare plus Medigap typically enroll in a standalone Part D plan to add drug coverage.

The Medigap open enrollment window

Your Medigap open enrollment period is a six-month window that begins the first month you are both age 65 or older and enrolled in Part B. During this window, insurers in most states must sell you any Medigap policy they offer in your state at standard rates — they cannot deny you coverage or charge higher premiums because of pre-existing health conditions.

Once this window closes, insurers in most states can apply medical underwriting, which means they may deny your application or charge significantly higher premiums based on your health history. A limited set of guaranteed-issue rights exist outside the open enrollment period — for example, when you lose employer or retiree coverage — but they apply only in specific circumstances and to specific plan types.

What Medicare Advantage is and how it works

Medicare Advantage (Part C) is an alternative way to receive your Medicare benefits through a private insurer approved by Medicare. Instead of Original Medicare paying providers directly, you receive your Part A and Part B coverage through an Advantage plan. Most Medicare Advantage plans also include prescription drug coverage (Part D) and may offer additional benefits not covered by Original Medicare, such as routine dental, vision, hearing, and transportation.

In exchange for these added benefits, Medicare Advantage plans typically involve a defined provider network. Most operate as Health Maintenance Organizations (HMOs) or Preferred Provider Organizations (PPOs):

• HMO plans generally require you to use in-network providers except in emergencies, and often require a primary care physician referral to see specialists.
• PPO plans allow out-of-network care at higher cost-sharing and typically do not require referrals.

Medicare Advantage plans set their own cost-sharing rules within CMS guidelines. Premiums vary — some plans have low or $0 monthly premiums, though you still pay the Part B premium. Plans have annual out-of-pocket maximums that cap your cost exposure within the network for covered services, which Original Medicare alone does not provide.

Medigap vs. Medicare Advantage: a direct comparison

Feature	Original Medicare + Medigap	Medicare Advantage
Provider access	Any Medicare-accepting provider nationwide	Network-based; out-of-network may be costly
Drug coverage	Requires separate Part D plan	Included in most plans
Out-of-pocket cap	Medigap covers most cost-sharing; no separate cap	Annual OOP max set by plan (CMS sets maximum allowed)
Monthly cost	Part B premium + Medigap premium (can be significant)	Part B premium + plan premium (often lower); higher point-of-service costs
Dental/vision/hearing	Not included; requires separate policies	Often included in MA plans
Travel/flexibility	Full nationwide flexibility	Generally limited to service area
Medical underwriting	During open enrollment window only	No underwriting; can enroll/switch annually

Documents and terms you’ll see

When reviewing Medigap and Medicare Advantage options, these terms appear frequently on plan materials and government resources:

• Medigap — also called Medicare Supplement insurance; the standardized private policies labeled A through N that fill Original Medicare’s gaps
• Medicare Advantage — Part C; private plans that bundle Part A, Part B, and usually Part D benefits
• Original Medicare — the federal government’s traditional Parts A and B program; the foundation that Medigap supplements
• Summary of Benefits — the standardized document Medicare Advantage plans must provide explaining covered services, cost-sharing, and network rules

Switching between paths

Switching from Medicare Advantage back to Original Medicare is generally possible during the Annual Enrollment Period (October 15 – December 7) or the Medicare Advantage Open Enrollment Period (January 1 – March 31). However, returning to Original Medicare does not automatically give you Medigap access at guaranteed rates — in most states you will face medical underwriting, and coverage may be denied or priced higher based on your health status. This asymmetry makes the initial choice significant.

What this means for planning

Neither Medigap nor Medicare Advantage is categorically better. The right fit depends on how often you use medical services, which providers you see, whether you travel, and what you can budget monthly versus at the point of service. The Medicare Basics guide covers the broader framework of Medicare’s parts and how these supplemental options connect to the overall program. Independent information is also available through state SHIP counselors and the Medicare Plan Finder at Medicare.gov.