Open enrollment mailers make Medicare sound like a coin flip between two boxes, but the real difference shows up in a hospital billing office, not a brochure.
Medicare Advantage is the all-in-one route.
You keep paying your Part B premium, and the private insurer running your plan usually adds extra benefits: dental, vision, hearing aids, gym memberships, sometimes a grocery allowance.
Many plans carry a $0 monthly premium, which is why roughly half of eligible Americans have chosen them, according to KFF.
Advantage plans work through networks, prior authorizations, and cost sharing that can reset every year.
A 2023 KFF analysis of federal data found that about 6 percent of prior authorization requests were fully or partially denied — and appeals sometimes reversed those decisions.
Medicare Supplement plans, also called Medigap, work differently.
You pay a private premium every month on top of Part B, and in exchange the plan picks up most or all of the 20 percent outpatient coinsurance that original Medicare leaves on your plate.
Any doctor or hospital that accepts Medicare generally accepts you.
The catch is the price tag and the timing.
Medigap premiums vary widely by state, age, and plan letter, and they rise over time.
More important, federal law only guarantees you the right to buy a Medigap policy without health questions during your six-month Medigap Open Enrollment Period, which starts the month you are 65 or older and enrolled in Part B.
Miss that window, and an insurer in most states can review your health history before selling you a policy.
A diabetes diagnosis or a recent cancer treatment can lead to a denial or a higher rate.
That single rule drives more Medicare decisions than any benefit comparison chart.
The math usually comes down to how you use care.
Someone who travels, sees specialists, or wants predictability may come out ahead with a supplement plus a standalone Part D drug plan, even at $150 to $250 a month.
Someone with tight cash flow who mostly wants routine care and low upfront costs may prefer Advantage — as long as they check whether their doctors are in network and how the plan handles prior authorizations.
Switching later is the part people underestimate.
You can move from original Medicare to Advantage fairly easily during enrollment periods.
Going the other direction, from Advantage back to a Medigap policy, often means passing medical underwriting, and a denial can leave you with original Medicare's uncapped 20 percent share and no supplement.
Before you decide, pull three things: your current doctor and hospital list, your prescription list with dosages, and last year's total out-of-pocket spending.
Then check each plan's formulary and network against them.
A free call to your State Health Insurance Assistance Program can walk you through the comparison without a sales pitch.
One more detail worth knowing: Advantage plans can change their networks, formularies, and copays every January.
A plan that fits this year is not guaranteed to fit next year, so the annual review matters as much as the original choice.
None of this is a prediction about your health or your bills — it is a map of how the two paths differ.
The honest takeaway is that neither option wins for everyone, and the marketing will never tell you which one fits you.
The people who end up frustrated are usually the ones who picked on premium alone and never read the network list.
Final Thoughts
Do the twenty-minute check now, because the window to switch without questions does not stay open forever.