Every fall, millions of Americans on Medicare face the same fork in the road, and the wrong turn can quietly drain a retirement account.
The two main paths—Medicare Advantage and Medicare Supplement plans—look similar on a brochure but behave nothing alike when a real medical bill lands.
The difference comes down to who controls the risk.
With Medicare Advantage, private insurers bundle your coverage into one plan, often with $0 premiums and extras like dental or gym memberships.
With a Supplement plan, also called Medigap, you keep original Medicare and pay a private insurer to cover most of what Medicare leaves behind.
A 2024 KFF analysis found Advantage enrollees faced an average out-of-pocket limit near $4,000, while many Medigap plans cap annual costs far lower once premiums are counted.
Advantage premiums can be near zero, but copays for hospital stays, scans, and specialists add up fast when you actually get sick.
Advantage plans usually run on HMOs or PPOs, meaning referrals, prior authorizations, and a list of in-network doctors.
A 2023 federal report found some plans denied prior authorization requests at rates above 10%, and denials spike for certain services.
Medigap has no network—any provider who takes Medicare takes you.
Then there's the enrollment window that trips up so many people.
You get a one-time, six-month Medigap open enrollment starting when 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 health history.
Switch from Advantage back to Medigap later, and you may be stuck.
Average Medigap Plan G premiums for a 65-year-old ran roughly $120 to $160 a month in many states in 2024, and they climb with age and medical inflation.
Advantage plans often advertise drug coverage built in, while Medigap users typically buy a separate Part D plan.
If you're healthy, want low premiums, and can live with a network, Advantage can work.
If you have chronic conditions, travel, or want predictable bills, Medigap's higher premium buys real peace of mind.
The catch is that the cheap choice today can become the expensive one tomorrow.
The real decision isn't about which plan is "better." It's about which risk you can stomach—steady monthly premiums or unpredictable bills when your health turns.
Run your own numbers with your actual prescriptions and doctors before you click enroll.
Our take: too many people pick Advantage for the $0 premium and never model a bad year.
Final Thoughts
Spend an hour with a licensed counselor at your State Health Insurance Assistance Program before you decide—it's free, and it's the cheapest financial advice you'll get this decade.