Every fall, millions of Americans on Medicare face the same confusing fork in the road.
On one side sits Medicare Advantage, advertised relentlessly with $0 premiums and free gym memberships.
On the other sits Medigap, the supplement plans you almost never see on TV.
The difference between them isn't just paperwork.
It's thousands of dollars out of your pocket.
Original Medicare pays 80% of covered costs, leaving you the other 20% with no cap.
A Medigap supplement picks up most of that gap, so a $150,000 hospital stay doesn't wreck your savings.
Medicare Advantage instead replaces Original Medicare with a private plan, often bundling drug coverage and extras like dental or vision, but it controls costs through networks, prior authorizations, and annual out-of-pocket limits that can run past $8,000 in 2025.
That out-of-pocket maximum is the number people miss.
Advantage plans cap your yearly exposure, which sounds protective until you realize the cap is high enough to hurt.
Medigap Plan G, the most popular supplement, has no network for doctors who accept Medicare, and it covers nearly all of that 20% once you pay a deductible of about $257 in 2025.
For someone who ends up in the hospital twice, the math can swing by $5,000 to $6,000 in a single year.
A Plan G premium can run $120 to $250 a month depending on your age, gender, and state.
Advantage premiums are often $0, though you keep paying the Part B premium either way.
That's why Advantage now covers just over half of all eligible beneficiaries, drawn in by the low sticker price and extra perks.
With most Medigap plans, you get a one-time guaranteed enrollment window when you first turn 65.
Wait past it, and insurers in most states can reject you or charge more based on your health history.
Switch to Advantage for a few years, develop a condition, and trying to move back to a supplement can become expensive or impossible.
A handful of states, including New York and Connecticut, offer year-round protections, but most don't.
If you're healthy, want predictable low premiums, and don't mind staying in-network, Advantage can work well.
If you have chronic conditions, travel, or simply want to avoid surprise bills, a supplement's higher monthly cost often buys real peace of mind.
The worst move is picking on premium alone and discovering the difference during a hospital stay.
My take: treat this like insurance, not a shopping deal.
The $0 premium is real, but it's not free, and the bill arrives later.
Final Thoughts
Run your own numbers, check whether your doctors are in-network, and look up your state's Medigap rules before you decide.