Every fall, millions of Americans on Medicare face the same fork in the road, and the wrong turn can quietly drain thousands from a retirement account.
The two main paths are Medicare Advantage (Part C) and Medicare Supplement plans, often called Medigap.
They behave nothing alike when the bills arrive.
Medicare Advantage is the all-in-one route.
Private insurers like UnitedHealthcare, Humana, and Aetna bundle your hospital, doctor, and drug coverage into a single plan, usually with a $0 or low monthly premium.
The trade-off hides in the fine print: copays, coinsurance, and an annual out-of-pocket maximum that can hit $8,850 for in-network care in 2025, and higher if you go out of network.
Dental, vision, and gym memberships are dangled as extras, and most plans throw in Part D drug coverage.
You keep original Medicare and buy a supplemental policy from a private insurer to cover what Medicare leaves behind.
The monthly premium is real money, often $100 to $200 or more depending on your age and state, and you still need a separate drug plan.
In exchange, most plans pick up nearly all of the 20% coinsurance that Medicare doesn't pay.
You see any doctor in the country who accepts Medicare.
A 2024 KFF analysis found that the average Medicare Advantage enrollee pays far less in premiums but can face thousands in cost sharing during a bad health year.
A Medigap enrollee pays more every month but faces a predictable, small bill when care happens.
If you're healthy, Advantage often wins on paper.
If you get cancer, need surgery, or land in a skilled nursing facility, the gap can swing the other way fast.
One catch trips up more people than any other: Medigap has near-guaranteed acceptance only during your six-month Medigap Open Enrollment Period, which starts the month you're 65 and enrolled in Part B.
Miss it, and insurers in most states can charge you more or reject you outright based on your health history.
Switching from Advantage back to Medigap later, after a diagnosis, can be brutally expensive or simply impossible.
Networks shift, formularies get rewritten, and a doctor you love can vanish from the directory by January.
Medigap Plan G or Plan N, by contrast, is the same standardized coverage no matter which insurer sells it, so shopping is mostly about price and rate increases, not benefits.
Check whether your doctors and hospitals are in the Advantage network for next year, not last year.
Add up your realistic worst-case year, not your best one.
And look at your state's Medigap rules, because a handful of states let you switch with fewer health questions.
The honest take: Medicare Advantage is a genuine bargain for healthy people who want low premiums and extras, and Medigap is expensive insurance you hope you never need.
But hope is not a plan, and the cost of guessing wrong lands hardest on the people who can least afford it.
Final Thoughts
Run your own numbers before open enrollment closes, because no brochure will do it for you.