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.
The gap between those two paths can run thousands of dollars a year, and picking wrong is one of the most expensive mistakes in retirement.
Original Medicare pays about 80% of covered costs, leaving you on the hook for the rest with no annual cap.
A Medigap supplement picks up most of that leftover, but you pay a monthly premium that often runs $100 to $200 or more.
Medicare Advantage replaces Original Medicare with a private plan, usually bundling drug coverage and extras like dental or vision, often for a low or $0 monthly premium.
That $0 premium is where people get tripped up.
Advantage plans still charge copays, coinsurance, and deductibles as you use care.
A hospital stay or a round of cancer treatment can trigger thousands in out-of-pocket costs, capped in 2025 at $9,350 for in-network care, and higher if you go out of network.
With a Medigap Plan G, by contrast, your costs are largely predictable once you pay the premium.
The trade-off is real in both directions.
Advantage plans can be cheaper if you're healthy and rarely see doctors, and many throw in perks that Original Medicare doesn't cover.
Supplements cost more upfront but tend to win for people with chronic conditions, frequent specialist visits, or a desire to see any doctor nationwide without referrals or prior authorizations.
One deadline matters more than any other.
Medigap insurers in most states can reject you or charge more based on health history once you're past your six-month Medigap Open Enrollment Period, which starts when you're 65 and enrolled in Part B.
Switch to Advantage first and try to come back later, and you may be medically underwritten or locked out entirely.
A handful of states, including New York and Connecticut, offer more protections, but most don't.
Formularies shift, networks shrink, and a plan that covered your doctors in January may not in January.
You can switch Advantage plans annually, but moving back to a supplement is the hard part.
The practical move: before you decide, list your doctors, your prescriptions, and how often you actually use care.
Then price both paths honestly, including the premiums you'd pay all year.
The cheaper-sounding option isn't always the cheaper one.
Our take: the system makes this harder than it should be, and the marketing leans heavily on that "$0 premium" hook.
If you can afford a supplement and want predictable costs, locking one in during your first enrollment window is often the safer bet.
Final Thoughts
Just run your own numbers, because your health and your budget are the only ones that count.