Medicare's annual enrollment window runs October 15 through December 7, and the single biggest decision facing the 68 million Americans on the program isn't which plan has the lowest premium.
It's whether to go with Medicare Advantage or original Medicare paired with a supplement policy.
The two paths look similar on a brochure and behave nothing alike once the bills arrive.
The headline numbers explain the confusion.
The average Medicare Advantage premium sits near $17 a month in 2025, according to KFF, and many plans advertise $0.
Original Medicare plus a Medigap Plan G runs $100 to $200 monthly depending on age and state, on top of the standard Part B premium of $185.
Advantage looks like the obvious bargain — until you read the fine print on what you actually pay when care gets expensive.
Advantage plans cap your yearly out-of-pocket spending, but those caps commonly land between $5,000 and $8,000 for in-network care, and far higher if you go out of network.
Medigap Plan G, by contrast, leaves you responsible only for the Part B deductible — about $257 in 2025 — and then covers essentially everything Medicare approves.
No prior authorizations for most services.
No surprise bills from an out-of-state specialist.
Investors and retirees tracking healthcare costs should pay attention to a quieter factor: prior authorization.
A 2023 KFF analysis found that Medicare Advantage plans denied 3.4 million prior authorization requests in a single year, about 6% of the total.
Most denials get overturned on appeal, but the appeals take time and paperwork.
For a retiree managing a chronic condition, that friction is the hidden cost the premium table never shows.
There's a catch that traps people every year: Medigap is hardest to buy after your first enrollment window.
In most states, insurers can reject you or charge more based on health history once you're past your six-month Medigap open enrollment period.
Advantage enrollees who develop a serious diagnosis often find they can't switch back affordably.
That asymmetry — easy to enter Advantage, hard to leave — is the part agents don't always emphasize.
If you have significant medical needs, travel often, or want predictable costs, the supplement's higher premium can pencil out fast once you clear a few thousand dollars in claims.
If you're relatively healthy, live near a strong local network, and want to keep monthly costs low, Advantage can work — as long as you read the drug formulary and provider list carefully rather than trusting the TV ad.
The practical move this fall: write down your actual 2024 medical costs, count your specialists, and check whether each is in-network under any Advantage plan you're considering.
Then compare that total against the Medigap premium plus deductible.
Run the math on your worst year, not your best one.
The open enrollment deadline doesn't negotiate, and the choice quietly compounds for a decade or more.
Final Thoughts
Treat the premium as the opening bid, not the final price.