Medicare Advantage vs Medigap: Pros and Cons in Plain English

If you are sorting out Medicare coverage, you will quickly run into two paths that sound similar and work very differently. Medigap is extra insurance that helps pay your share of costs in Original Medicare — copayments, coinsurance, and deductibles — while letting you use any doctor or hospital that takes Medicare anywhere in the U.S. Medicare Advantage is a different way to get your Medicare coverage: it usually asks you to stay in a plan’s network, may require a referral to see a specialist, and puts a yearly cap on what you pay for covered services. You can’t have both. And the piece people most often learn too late is that the Medigap Open Enrollment Period is a one-time 6-month window starting the first month you have Part B and are 65 or older — during it, you can’t be denied a policy because of pre-existing health problems.

What Medicare Advantage and Medigap Actually Are

These two options get compared side by side constantly, but they are not the same kind of product. One sits on top of Original Medicare. The other is a different way to receive your Medicare coverage altogether.

That distinction explains almost every difference that follows — including why you cannot sign up for both.

Medigap: extra insurance that fills in Original Medicare’s gaps

Medicare Supplement Insurance, usually called Medigap, is extra insurance you may be able to buy from a private insurance company to help pay your share of out-of-pocket costs in Original Medicare — things like copayments, coinsurance, and deductibles.

Generally, you must have Original Medicare — Part A (hospital insurance) and Part B (medical insurance) — before you can buy a Medigap policy. Medigap does not replace Parts A and B. It sits alongside them and picks up costs they leave to you, such as the 20% coinsurance on Part B-covered services.

Medicare Advantage: a different way to get your Medicare coverage

A Medicare Advantage Plan is an alternative to Original Medicare for how you get your health coverage. Plans must cover what Original Medicare covers. Anything beyond that — and how much you pay for any given service — varies by plan, so the only reliable source is that specific plan’s Evidence of Coverage document or a call to the plan itself.

With Medicare Advantage, you still pay the monthly Part B premium, and you may also pay the plan’s premium. Most plans include Medicare drug coverage (Part D), so there’s usually no separate Part D premium.

Why you can’t have both

Medicare.gov is direct about this: if you’re in a Medicare Advantage Plan, you can’t buy Medigap to cover your out-of-pocket costs. Medigap only works with Original Medicare.

So the real decision isn’t “which add-on?” It’s “do I want Original Medicare with something helping pay my share, or do I want a plan that handles my coverage with its own rules and its own cap?”

The Side-by-Side Comparison, Straight From Medicare.gov

Medicare.gov publishes its own comparison of Original Medicare and Medicare Advantage. Here is what it says on the points that matter most, with the Medigap piece added where it applies.

What you’re comparing	Original Medicare (with the option to buy Medigap)	Medicare Advantage
Doctor & hospital choice	Any doctor or hospital that takes Medicare, anywhere in the U.S. You may pay more if your doctor doesn’t accept assignment.	You may need to use doctors and providers in the plan’s network and service area for non-emergency care. Some plans cover non-emergency care out of network, but it may cost more.
Referrals to specialists	In most cases you don’t need a referral.	You may need a referral to see a specialist.
Your share of costs	For Part B-covered services, you usually pay 20% of the Medicare-approved amount after you meet your deductible.	Out-of-pocket costs vary. Plans may have different out-of-pocket costs for certain services.
Premiums	Monthly Part B premium; a separate Part D premium if you join a Medicare drug plan.	Monthly Part B premium, and you may also pay the plan’s premium. Most plans include Part D.
Yearly out-of-pocket limit	None, unless you have supplemental coverage like Medigap, or other coverage such as Medicaid, employer, retiree, or union insurance.	Plans have a yearly limit on what you pay for covered Medicare services, which may include different limits for in-network and out-of-network care. Once you reach the limit, you pay nothing for covered services for the rest of the year.
Can you add Medigap?	Yes — you can choose to buy Medigap to help pay out-of-pocket costs Medicare doesn’t cover, like your 20% coinsurance.	No. You can’t buy Medigap to cover your out-of-pocket costs.

“Anywhere in the U.S.” on that Medicare.gov page includes the 50 states, the District of Columbia, Puerto Rico, the U.S. Virgin Islands, Guam, the Northern Mariana Islands, and American Samoa.

What “accepts assignment” means

Assignment means a doctor or supplier agrees to accept the Medicare-approved amount as full payment for a covered service. Medicare.gov notes that with Original Medicare you may pay more if your doctor doesn’t accept assignment — so it’s a fair question to ask at the front desk before an appointment.

What the out-of-pocket limit does and doesn’t do

The yearly limit in a Medicare Advantage Plan applies to covered Medicare services, and plans may set different limits for in-network and out-of-network care. Once you hit your plan’s limit, you pay nothing for covered services for the rest of the year.

Original Medicare on its own has no such yearly cap. That’s the gap Medigap is designed to help with. Neither arrangement caps everything — services Medicare doesn’t cover at all are a separate matter.

The Trade-Offs, Honestly Stated

Here’s what the official comparison actually shows when you line the trade-offs up. Neither column is “better” — they trade different things.

Where Medigap with Original Medicare has the edge

• Freedom of provider: any doctor or hospital that takes Medicare, anywhere in the U.S.
• In most cases, no referral needed to see a specialist.
• Help paying the predictable gaps — copayments, coinsurance, and deductibles.
• Standardization: all Medigap policies are standardized, so policies with the same letter offer the same basic benefits no matter where you live or which company sells them. There are 10 lettered types offered in most states: A–D, F, G, and K–N. Price is the only difference between same-letter policies from different companies.

The costs and catches on the Medigap side

• You pay a separate premium for the Medigap policy on top of your Part B premium.
• Medigap doesn’t include drug coverage, so you’d join a separate Medicare drug plan and pay a separate Part D premium.
• The big one: after your one-time 6-month Medigap Open Enrollment Period ends, you may not be able to buy a Medigap policy at all, or it may cost more.
• In some states, you may be able to buy another type of policy called Medicare SELECT, which has its own rules.

Where Medicare Advantage has the edge

• A yearly limit on what you pay for covered Medicare services — a ceiling Original Medicare alone doesn’t have.
• Most plans include Medicare drug coverage, so there’s no separate Part D premium to manage.
• Plans must cover what Original Medicare covers, and some offer benefits beyond that. What those are, and what they cost, varies by plan — check the plan’s Evidence of Coverage or call the plan.

The costs and catches on the Medicare Advantage side

• You may need to use doctors and providers in the plan’s network and service area for non-emergency care. Out-of-network coverage, where offered, may cost more.
• You may need a referral to see a specialist.
• Out-of-pocket costs vary, and plans may charge different amounts for different services.
• You can’t buy Medigap to cover your out-of-pocket costs while you’re in a Medicare Advantage Plan.

The Timing Rule People Miss

If you remember one thing from this page, make it this one.

You get a 6-month Medigap Open Enrollment Period that starts the first month you have Medicare Part B and you’re 65 or older. During that window, you can enroll in any Medigap policy and the insurance company can’t deny you coverage due to pre-existing health problems.

That period is a one-time enrollment. It does not repeat every year the way the Medicare Open Enrollment Period does. After it ends, you may not be able to buy a Medigap policy, or it may cost more.

Think of it like a door that opens once when you first qualify. Walk through it or don’t — but know that it closes, and that the rules on the other side are different.

What this means practically

It means the Medigap question is worth answering early, not after a health problem makes you wish you had. Mark the month your Part B coverage starts on a calendar and count six months forward.

It also means that someone who chooses Medicare Advantage first and later wants Medigap may face a different set of rules than they would have during that first window. Before you assume you can switch later, confirm the specifics for your situation with 1-800-MEDICARE or a free State Health Insurance Assistance Program (SHIP) counselor.

Where to find this year’s dollar figures

Medicare’s cost amounts — the Part B premium, the yearly Part B deductible, Part A amounts — change every year. This page deliberately doesn’t quote them, because a number that was right last year isn’t right now.

Look them up directly at Medicare’s costs page. That’s the authoritative source, and it’s updated each year.

How to Work Through the Decision

There’s no universally right answer here, and anyone who tells you otherwise is selling something. What there is: a short list of questions whose answers are specific to you.

Start with your doctors

Write down every doctor and hospital you want to keep. With Original Medicare you can use any of them that takes Medicare. With a Medicare Advantage Plan, you may need providers in the plan’s network and service area for non-emergency care — so the question becomes whether your doctors are in that particular plan’s network, which only the plan can tell you.

Think about where you spend your year

If you travel often, split your time between two states, or spend months near grandchildren, the provider-choice difference matters more than it does for someone who sees the same three doctors in one town. Original Medicare’s access applies anywhere in the U.S., including the District of Columbia, Puerto Rico, the U.S. Virgin Islands, Guam, the Northern Mariana Islands, and American Samoa.

Account for your prescriptions — and everything else you take

With Original Medicare plus Medigap, drug coverage comes from a separate Medicare drug plan with its own premium. Most Medicare Advantage plans include it.

While you’re making that list, bring your supplements too. Many common ones interact with prescription medicines, and your pharmacist can flag problems in a few minutes — our guide to supplements and medications walks through the most common conflicts. If you’re reviewing an omega-3 habit alongside a blood thinner, how much fish oil a 65-year-old should take covers the dose question.

Read the actual documents

For any Medicare Advantage Plan, the Evidence of Coverage is the binding document — not a brochure, not a mailer, not a television ad. It spells out networks, referrals, costs, and limits. Call the plan directly with questions.

For Medigap, remember that same-letter policies offer the same basic benefits regardless of which company sells them, and that price is the only difference between those identical-letter policies. That makes comparison simpler than it looks at first.

Where to Get Official Answers

Medicare is a federal program, and its own channels are free, unbiased, and the only place these rules are definitive.

• Medicare.gov — the official site for coverage rules, enrollment periods, and current-year costs.
• 1-800-MEDICARE (1-800-633-4227), TTY 1-877-486-2048 — live help, available 24 hours a day, 7 days a week (except some federal holidays).
• Your State Health Insurance Assistance Program (SHIP) — free, one-on-one counseling from trained local counselors who don’t sell anything. Medicare.gov’s talk to someone page will connect you to your state’s program.

And on the health side of the ledger: if a particular test, treatment, or service is part of what’s driving your decision, ask your doctor whether it’s medically necessary for you — Medicare coverage often hinges on that. If you’re also rethinking vitamins or supplements while you reorganize your health care, talk with your doctor or pharmacist before changing anything, and see our overview of what supplements a 70-year-old woman should take for a starting framework to bring to that conversation.

Sources:

• Compare Original Medicare & Medicare Advantage — Medicare.gov — Source for doctor and hospital choice, referrals, cost sharing, premiums, yearly out-of-pocket limits, and the rule that you can’t buy Medigap while in a Medicare Advantage Plan.
• What’s Medicare Supplement Insurance (Medigap)? — Medicare.gov — Definition of Medigap and the requirement to generally have Part A and Part B to buy a policy.
• Get Medigap Basics — Medicare.gov — Source for the one-time 6-month Medigap Open Enrollment Period, standardization of lettered plans A–D, F, G, K–N, and Medicare SELECT.
• Medicare costs — Medicare.gov — Where readers find current-year Part B premium and deductible amounts, which change annually.
• Talk to someone — Medicare.gov — Source for 1-800-MEDICARE, TTY number, and free State Health Insurance Assistance Program counseling.