Every fall, millions of Americans on Medicare face the same confusing choice: stick with Original Medicare plus a supplement, or switch to a Medicare Advantage plan with that tempting $0 monthly premium.
The ads make Advantage look like a no-brainer.
Original Medicare (Parts A and B) pays roughly 80% of covered costs, and a Medigap supplement picks up most of the rest.
Medicare Advantage, by contrast, is a private plan that replaces Original Medicare and often bundles in dental, vision, and hearing — but it controls which doctors you see and how much you pay when you actually get sick.
Advantage plans advertise low or $0 monthly payments, but they come with copays, coinsurance, and annual out-of-pocket maximums that can run past $8,000 in 2024.
A Medigap Plan G might cost $130 to $200 a month depending on your state and age, yet once you pay the premium, your share of most covered medical bills is often close to nothing.
That gap matters most when something serious happens.
A few days in the hospital, a cancer diagnosis, or a skilled nursing stay can push Advantage enrollees toward thousands in cost sharing.
Supplement holders typically pay far less at the point of care because the plan absorbs the difference.
There's also a timing trap that catches people off guard.
In most states, you get a one-time Medigap "guaranteed issue" window that starts when you first enroll in Part B at 65.
During that window, an insurer can't charge you more or deny you coverage because of your health history.
Wait too long, and a supplement can become expensive or outright unavailable if you develop a condition.
If you're healthy, take few prescriptions, and want predictable low premiums with extras like gym memberships or dental, the trade-off can work in your favor.
The catch is that you're betting your health stays steady — and health rarely cooperates with a budget spreadsheet.
If you're already in an Advantage plan and want to switch back to Original Medicare with a supplement, you may face medical underwriting in most states.
A handful of states, including New York and Connecticut, offer more lenient rules year-round, but the rest can leave you stuck.
Check whether your doctors and hospitals are in the Advantage network.
Add up your prescriptions under each plan's specific formulary, not a generic estimate.
And read the plan's annual out-of-pocket maximum — that's your real worst-case number, not the premium.
The open enrollment window for 2025 coverage runs through December 7, and Advantage enrollees get a second chance to switch between January 1 and March 31.
Use that time to compare actual costs, not marketing promises.
Our take: the cheapest premium is rarely the cheapest plan.
For anyone with ongoing health needs or a desire to see any specialist without referrals, a supplement's higher monthly cost often buys real peace of mind.
Final Thoughts
Run your own numbers, but don't let a $0 headline make the decision for you.