If you're turning 65 or reviewing your coverage right now, you're staring down one of the most expensive decisions in retirement.
Medicare Advantage and Medicare Supplement plans sound similar on a brochure, but they work in completely different ways.
Pick the wrong one for your health situation, and you could be on the hook for thousands of dollars a year.
Medicare Advantage (Part C) replaces Original Medicare with a private insurance plan, often bundling in drug coverage, dental, vision, and gym memberships.
Many plans advertise $0 monthly premiums, which makes them tempting.
Medicare Supplement plans, also called Medigap, don't replace anything.
They sit behind Original Medicare and cover most of the gaps, like copays, coinsurance, and deductibles.
The trade-off comes down to premiums versus out-of-pocket costs.
Advantage plans tend to have low or zero monthly premiums but charge you each time you see a doctor, get a test, or spend a night in the hospital.
There's also an annual out-of-pocket maximum, which in 2024 sits at $8,850 for in-network care.
Medigap plans run higher monthly premiums, often $100 to $200 or more depending on your age and state, but once you pay that premium, most plans cover nearly everything Medicare approves.
That difference matters most when you actually get sick.
A Medicare Advantage patient with a serious diagnosis can rack up copays for specialists, scans, and hospital stays until they hit that cap.
A Medigap enrollee with Plan G, one of the most popular options, typically pays just the Part B deductible and then very little else.
For someone managing cancer, heart disease, or frequent specialist visits, that gap can run into the thousands.
There's another wrinkle people miss: network restrictions.
Advantage plans usually use HMOs or PPOs, meaning you may need referrals, stay in-network, or get prior authorization for procedures.
Medigap works with any provider in the country who accepts Medicare, which is most of them.
If you travel or snowbird between states, that flexibility can be worth real money.
Drug coverage is a separate piece of the puzzle.
Most Advantage plans include Part D prescriptions built in.
If you choose Medigap, you'll need to buy a standalone Part D plan, which adds another premium but often gives you more control over your pharmacy choices.
You get a one-time guaranteed acceptance window when you first enroll in Medicare Part B, usually six months.
During that window, insurers can't turn you down or charge more because of your health history.
Miss it, and you may face medical underwriting later, which means a plan can reject you or price you higher for conditions like diabetes or heart disease.
Advantage plans don't have that problem, since you can switch into one most years during Open Enrollment.
If you're healthy, rarely see doctors, and want the lowest monthly cost, an Advantage plan can make sense.
If you have chronic conditions, see specialists, or want predictable costs and nationwide freedom, Medigap is often the safer bet, even with the higher premium.
The real trap is choosing a $0 premium plan today and discovering the copays later, when switching to Medigap may no longer be an option without underwriting.
My take: run the math on your worst-case year, not your best-case one.
A plan that saves you $150 a month but leaves you exposed to an $8,000 hospital bill isn't really saving you anything.
Final Thoughts
Talk to a licensed broker who can pull your actual drug list and doctors before you decide, because this is one enrollment choice you can't easily undo.