Choosing between Medicare Advantage and a Medigap supplement feels like a coin flip until you read the fine print on what each one actually pays.
Original Medicare covers about 80% of most medical costs and leaves you with the rest.
A supplement, often called Medigap, picks up most of that leftover share.
Medicare Advantage is different: private insurers take over your coverage, often bundling in dental, vision, and drug plans, but you agree to their network, their prior authorizations, and their rules.
The trade-off shows up in the monthly math.
A Medigap Plan G can run $120 to $200 a month depending on your state and age, on top of the standard Part B premium.
Medicare Advantage often advertises $0 premiums, which looks like a steal, until you hit the copays for a hospital stay or a specialist visit.
That gap matters most when you actually get sick.
A Medicare Advantage plan may cap your annual out-of-pocket costs around $8,850 in 2025, while a Plan G supplement leaves you paying only the Part B deductible, roughly $257, plus your premium.
For someone facing a serious diagnosis, those numbers can differ by thousands.
Advantage plans use HMOs and PPOs, so if your cardiologist isn't in-network, you may pay more or switch doctors entirely.
Medigap works with any provider nationwide who accepts Medicare, which is a real comfort if you travel or split time between states.
The catch with supplements is that insurers can reject you.
Outside your initial enrollment window, a Medigap company can deny coverage or charge more because of your health history.
Advantage plans must accept you during open enrollment, so they're often the only door available to people with pre-existing conditions.
Most Advantage plans include Part D, but you can't easily add a standalone drug plan to Medigap without paying separately.
If your medications are expensive, run both scenarios through the Medicare Plan Finder before deciding.
First, list your doctors and check which plans include them.
Second, estimate your typical year of care, not a perfect year.
Third, compare the worst-case annual total, not the monthly premium.
Fourth, check whether you can switch later without underwriting, because in most states you can't.
There's a quiet detail many people miss: you can try Medicare Advantage and switch back to Original Medicare during the annual enrollment window, but getting a supplement afterward may require passing medical underwriting.
Some states, including New York and Connecticut, offer more flexibility, but most don't.
Advantage tends to win for healthy people who want low premiums and extra perks.
Supplements tend to win for people who want predictable costs and the freedom to see any Medicare doctor.
The real mistake is choosing based on the advertised premium alone.
A $0 plan that costs you $6,000 in a bad year isn't cheap, and a $180 monthly supplement that keeps your worst-case bill under $300 may be the better deal.
My take: treat this as a bet on your future health, not your current health.
If you can afford the premium and qualify, a supplement buys you predictability that's hard to replace.
Final Thoughts
If the premium strains your budget, an Advantage plan can still work, but read the out-of-pocket cap and network list before you sign.