Choosing between Medicare Advantage and a Medigap supplement is the single biggest health-cost bet most Americans over 65 will ever make, and the gap between the two paths can run into thousands of dollars a year.
The decision window for 2025 coverage runs through December 7, so the clock is already ticking.
Yet surveys consistently show a large share of enrollees pick a plan based on the premium alone — the number that shows up in the TV ad — without pricing out what happens when they actually get sick.
Original Medicare (Parts A and B) pays about 80% of covered costs and leaves you on the hook for the rest, with no annual cap.
A Medigap supplement plugs most of that hole, but you pay a monthly premium for it — often $100 to $200 or more depending on your state and plan letter.
Medicare Advantage, by contrast, is a private plan that replaces the way you get Original Medicare, frequently with a $0 premium, but it comes with networks, prior authorizations, and a hard annual out-of-pocket ceiling that in 2025 sits at $9,350 for in-network care.
That $0 premium is where the math gets sneaky.
Advantage plans advertise low or no monthly cost, then recoup through copays for specialist visits, hospital stays, and procedures.
A healthy 67-year-old may spend almost nothing.
A 72-year-old managing diabetes, heart issues, and a couple of specialist referrals can blow past what a supplement would have cost — and they can't easily switch back.
In most states, Medigap insurers can deny you or charge more once you're past your initial enrollment window, so the cheap choice early can become a locked door later.
The under-discussed trap is the trial right.
If you start with Advantage and want out within the first 12 months, federal rules give you a guaranteed shot at a Medigap plan in most situations.
Miss that window and you're underwriting — meaning a health questionnaire, and a real chance of rejection.
Consumer advocates say this is the moment where retirees most often call for help and find out their options have quietly narrowed.
So what should you actually do before December 7?
First, list every drug you take and check each plan's formulary, not just the premium.
Second, price your realistic worst year, not your best one — add up copays, coinsurance, and the out-of-pocket max.
Third, check whether your doctors and hospitals are in the Advantage network, because "in network" can change every January.
If you travel often or split time between states, Advantage networks can be a headache, while Original Medicare plus a supplement generally follows you anywhere in the country that accepts Medicare.
If you're cost-constrained month to month and rarely see specialists, the low-premium route can genuinely make sense.
There's no universal right answer — but there is a wrong method, and that's deciding on the sticker price alone.
Our take: treat this like a mortgage, not a subscription.
The monthly number is the least important figure on the page.
Final Thoughts
Spend 30 minutes with a calculator and your medication list before the deadline, because the plan you pick now is the one you may be stuck defending for years.