Choosing between Medicare Advantage and a Medigap supplement is one of the most expensive decisions many retirees will ever make, and most people get almost no help making it.
Pick wrong, and you could be locked out of the plan you actually want for the rest of your life.
Medicare Advantage (Part C) replaces Original Medicare with a private plan, often bundling drug coverage and extras like dental or gym memberships.
You typically pay a low or $0 monthly premium, but you accept a network of doctors and prior authorizations.
A Medigap supplement, by contrast, sits on top of Original Medicare and picks up much of what Medicare doesn't.
The trade-off: higher monthly premiums, but you can see almost any provider nationwide.
Advantage plans can change their provider networks and drug formularies every single year, so the doctor you love may vanish from the list next January.
They also lean heavily on prior authorization, which can delay or deny care.
Supplements are far more predictable, but you'll pay for that predictability every month.
The single most important rule: if you choose Medicare Advantage when you first turn 65 and later want to switch to a supplement, most states let insurers medically underwrite you.
That means they can reject you or charge more because of your health history.
In most states, your guaranteed right to buy a Medigap policy without health questions exists only during that first six-month window around your 65th birthday.
Miss it, and a cancer diagnosis or heart condition can slam the door.
A few states, including New York, Connecticut, Massachusetts, and Maine, have year-round guaranteed-issue rules that protect you longer.
If you live elsewhere, that initial window is your best shot.
If you're healthy, travel little, and want to minimize premiums now, an Advantage plan can look appealing.
If you have chronic conditions, see specialists, or split time between states, a supplement often wins despite the higher premium.
Run your actual prescriptions and doctors through both options before deciding, not after.
Advantage plans flood mailboxes and airwaves every fall with $0 premium pitches, and some ads blur the line between the two products.
A "$0 premium" Advantage plan can still hit you with copays for hospital stays, scans, and specialist visits that add up fast.
Open Enrollment for 2025 coverage runs through December 7, and the Medicare Plan Finder at medicare.gov lets you compare plans side by side.
If you're already in an Advantage plan, check whether your doctors and drugs are still covered before the deadline passes.
The bottom line: this isn't a decision to rush in the last week of enrollment or to base on whichever commercial you saw last.
The choice you make at 65 can follow you for decades, and the window to keep your options open may be smaller than you think.
Final Thoughts
Do the homework now, while you still have the leverage to choose.