Once you understand that original Medicare has coverage gaps, the next question is how to address them. Most people end up choosing between two broad approaches: adding Medigap to original Medicare, or switching to Medicare Advantage. These work very differently, and the choice has real consequences for how you receive care.
This article explains what each one is and how they compare. It does not recommend one over the other - that is a personal decision that depends on your health use, finances, and where you live.
What is the core difference between Medigap and Medicare Advantage?
Medigap supplements original Medicare - you keep Parts A and B and Medigap covers some or all of the cost-sharing Medicare leaves to you. Medicare Advantage replaces original Medicare - you receive your benefits through a private plan instead. According to Medicare.gov, you cannot have both at the same time.
The simplest way to understand the difference is this:
- Medigap supplements original Medicare. You keep Parts A and B, use them as your primary coverage, and Medigap pays some or all of the cost-sharing that Medicare leaves to you.
- Medicare Advantage replaces original Medicare. Instead of using Parts A and B directly, you receive your Medicare benefits through a private insurance plan that has contracted with Medicare.
According to Medicare.gov, you cannot have both Medigap and Medicare Advantage at the same time. They are two different paths, not layers you can stack.
How does Medigap work?
Medigap is sold by private insurers but standardized by the federal government. Plans are identified by letters A through N, and every plan with the same letter offers the same core benefits regardless of which company sells it. You keep original Medicare, use it at the point of care, and Medigap pays some or all of the remaining cost-sharing - with no network restrictions in most cases.
Medigap policies are sold by private insurance companies, but they are standardized by the federal government. According to Medicare.gov, each plan is identified by a letter (A through N), and every policy with the same letter offers the same core benefits regardless of which company sells it. What varies is the monthly premium and, to some extent, the company's service and financial stability.
With Medigap, you generally continue to see any provider who accepts Medicare - there are typically no network restrictions. You use your Medicare card at the doctor's office or hospital, and Medicare pays its share. Then Medigap pays some or all of the remaining cost-sharing, depending on which plan letter you have.
Medigap does not include prescription drug coverage. If you have Medigap, you need a separate Part D plan for medications.
What Medigap does not cover at all, regardless of plan letter: long-term care, routine dental, routine vision, hearing aids, and private-duty nursing. These remain gaps even with Medigap.
How does Medicare Advantage work?
Medicare Advantage plans are offered by private insurers approved by Medicare. They must cover everything original Medicare covers, but deliver it through their own network and plan structure. Most plans include drug coverage and often add dental, vision, and hearing benefits, but they come with network restrictions and prior authorization requirements that do not exist with original Medicare.
Medicare Advantage plans are offered by private insurance companies that Medicare has approved. According to Medicare.gov, these plans are required to cover everything original Medicare covers, but they deliver that coverage through their own network and plan structure rather than through traditional Medicare.
Most Medicare Advantage plans include prescription drug coverage, so a separate Part D plan is generally not needed. Many plans also offer added benefits that original Medicare does not cover - things like routine dental, vision, hearing, and fitness programs. The extent of these extras varies significantly from plan to plan and by geography.
The trade-offs with Medicare Advantage:
- Network restrictions. Most plans require you to use providers within their network. HMO plans generally require you to stay in-network except for emergencies. PPO plans offer more flexibility but typically charge more for out-of-network care.
- Prior authorization. Many services require advance approval from the plan before they are covered. This is different from original Medicare, which generally does not require prior authorization for covered services.
- Plan structure varies by area. What is available, what is included, and what it costs differs significantly depending on where you live. A plan that is excellent in one county may not be available or may look very different in another.
How do Medigap and Medicare Advantage compare in practice?
Neither option is objectively better. Medigap typically offers more predictable out-of-pocket costs and broader provider access, but higher premiums. Medicare Advantage often has lower premiums and extra benefits, but involves network restrictions, prior authorization, and cost-sharing that can vary based on the services you use.
A 2022 report by the HHS Office of Inspector General found that Medicare Advantage plans denied a notable share of prior authorization requests that appeared to meet Medicare coverage criteria, and that some denials delayed or prevented access to care that Medicare would otherwise cover. This is worth understanding before enrolling - not as a reason to avoid Advantage plans, but as a reason to ask a plan about its prior authorization process and appeal rights before you commit.
Neither option is objectively better. They involve genuine tradeoffs that matter differently depending on who you are.
Cost predictability. Medigap typically offers more predictable out-of-pocket costs because it covers defined cost-sharing amounts. Medicare Advantage plans may have lower premiums but can involve more variable cost-sharing depending on the services you use.
Provider flexibility. Original Medicare with Medigap generally allows you to see any provider who accepts Medicare, which is most providers nationwide. Medicare Advantage networks can be narrower, which matters most if you travel frequently, spend time in multiple states, or have established care relationships with specific specialists.
Extra benefits. Medicare Advantage plans often include dental, vision, and hearing benefits that original Medicare and Medigap do not cover. The value of these benefits depends on how much you actually use them and what the plan's limits are.
Geography. Medicare Advantage plan availability and quality varies significantly by county. In some areas there are many strong options; in rural areas options may be limited.
Can You Switch Between Them?
You can switch between these two paths, but timing matters significantly. Switching from Medicare Advantage back to original Medicare is allowed during certain enrollment periods, but if you want to add Medigap at that point, you may face medical underwriting in most states - meaning insurers can charge more or decline coverage based on your health history.
You can switch from Medicare Advantage back to original Medicare during the annual Medicare Advantage Open Enrollment Period (January 1 to March 31 each year) or during the fall Annual Enrollment Period. However, according to Medicare.gov, if you want to add Medigap after leaving Medicare Advantage, you may not have guaranteed issue rights in most states - meaning insurers may be able to use medical underwriting and could charge you more or decline coverage based on your health history.
This is one reason the timing of when you first enroll in supplemental coverage matters significantly. See our article on Medigap open enrollment and guaranteed issue rights for more detail.
Getting Help Deciding
A SHIP (State Health Insurance Assistance Program) counselor can walk you through the specifics of what is available in your area, what it would cost given your situation, and how each option compares - at no cost and without selling you anything. This is often the most practical starting point before comparing specific plans.
One additional note worth carrying into any conversation with a broker or SHIP counselor: ask specifically about the prior authorization process for any Advantage plan you are considering. Documented concerns about denial rates and approval delays are worth understanding clearly - particularly as healthcare needs tend to increase with age.
Find your local SHIP counselor at shiphelp.org or by calling 1-800-677-1116. A licensed independent Medicare insurance broker can also help you compare specific plan options in your area.
Plan availability, benefits, and costs change each year and vary by location. Visit medicare.gov or speak with a SHIP (State Health Insurance Assistance Program) counselor for information specific to your area. A SHIP counselor can give you personalized guidance on Medicare options at no cost. Find yours at shiphelp.org.