Every fall, millions of Americans on Medicare face the same confusing fork in the road: stick with Original Medicare plus a supplement plan, or switch to a Medicare Advantage plan with its tempting $0 premium ads.
Pick wrong and you could be on the hook for thousands of dollars in bills you never saw coming.
Original Medicare (Parts A and B) pays roughly 80% of covered costs, leaving you with 20% — and there's no annual cap on that 20%.
A Medigap supplement plan picks up most or all of that gap, but you pay a monthly premium for the privilege.
Medicare Advantage, by contrast, is a private insurance plan that replaces Original Medicare, often bundles in dental, vision, and drug coverage, and frequently advertises a $0 monthly premium.
That $0 premium is where people get burned.
Advantage plans can charge copays for hospital stays, specialist visits, and even chemotherapy, and the out-of-pocket maximum can run as high as $9,350 in-network for 2025, according to KFF.
Medigap Plan G, the most popular supplement, caps your exposure far lower — you mostly just cover the Part B deductible, which is $257 this year.
The catch with Medigap is the price tag and the timing.
A Plan G policy can cost $100 to $200+ per month depending on your age and state, on top of your Part B premium.
And here's the part that trips people up: if you don't enroll in Medigap during your initial six-month window, insurers in most states can deny you or charge more based on your health history.
Miss that window and you may be locked out for good.
That means prior authorizations, referrals, and provider lists that can change year to year.
If your cardiologist drops your plan in January, you're scrambling.
With Original Medicare plus Medigap, you can see almost any doctor in the country who accepts Medicare — no referrals, no network surprises.
If you're healthy, cost-conscious, and comfortable with a network, an Advantage plan can work well and save you real money on premiums.
If you have chronic conditions, travel often, or want predictable costs and total freedom of providers, Medigap plus a standalone Part D drug plan is usually the safer bet — if you can afford the monthly premium.
Going from Advantage back to Original Medicare is allowed, but buying a Medigap policy afterward often requires passing medical underwriting in most states.
A handful of states, including New York and Connecticut, offer more flexible "guaranteed issue" rules year-round — check your state's rules before assuming you can move freely.
Add up premiums, estimate your worst-case year of medical costs, and list your must-have doctors.
Don't let a flashy $0 premium ad make the decision for you.
Our take: the cheapest plan on the flyer is rarely the cheapest plan in a bad year.
Final Thoughts
Spend an hour with a licensed broker or your state's SHIP counselor before you lock in — it's free, and it could save you a fortune.