Every fall, millions of Americans on Medicare face the same confusing choice, and the wrong pick can quietly cost them thousands of dollars a year.
The decision comes down to two very different paths: Medicare Advantage or a Medicare Supplement plan.
The two sound interchangeable in ads, but they work nothing alike.
Advantage plans, also called Part C, replace Original Medicare with a private insurer's network.
Supplement plans, often called Medigap, sit on top of Original Medicare and pick up the bills it leaves behind.
Here's where the money math gets interesting.
Advantage plans often advertise $0 premiums, and that headline is real.
The catch is what comes later: copays for doctor visits, hospital stays, and specialist care that can add up fast if your health takes a turn.
You pay a monthly premium that can run well over $100 depending on your age, state, and plan letter.
In exchange, your out-of-pocket costs become far more predictable, and most plans let you see any doctor nationwide who accepts Medicare.
Advantage enrollees typically face networks, prior authorizations, and annual caps on what they pay.
Medigap enrollees usually don't deal with networks at all, but they pay that premium whether they use care or not.
Timing matters more than almost anything else here.
If you sign up for Medigap during your six-month Medigap Open Enrollment Period, which starts when you're 65 and enrolled in Part B, insurers generally can't reject you or charge more because of health problems.
Miss that window, and in most states you can be denied coverage or quoted a higher rate based on your medical history.
That single deadline has locked countless retirees into Advantage plans they didn't really want.
Advantage has its own perks worth weighing.
Many plans bundle dental, vision, hearing, and even gym memberships, and some include Part D drug coverage at no extra charge.
If you're healthy, take few medications, and don't mind staying in-network, the low premium can genuinely save money.
Prescription costs deserve a hard look either way.
A drug that's cheap on one plan can be expensive on another, so it pays to check your specific medications against each plan's formulary before you commit.
Going from Advantage to Medigap later usually means passing medical underwriting, and a single diagnosis can slam that door.
Going from Medigap to Advantage is easier, since Advantage plans must accept most applicants.
The practical move is to estimate your worst year, not your best one.
Add up premiums plus the maximum out-of-pocket limit on each Advantage plan you're considering, then compare that to a Medigap premium plus the Part B deductible and any drug costs.
A healthy 65-year-old might come out ahead on Advantage for years.
A 72-year-old managing two chronic conditions could blow past that Advantage out-of-pocket cap and wish they'd paid the Medigap premium all along.
Free counseling is available and underused.
State Health Insurance Assistance Programs, or SHIPs, offer unbiased one-on-one help, and Medicare's own Plan Finder tool lets you plug in your drugs and doctors to compare real numbers.
Open Enrollment for 2026 runs October 15 through December 7, 2025, so the clock is already ticking.
Anyone currently on Medicare can switch Advantage plans or move between Advantage and Original Medicare during that window, though Medigap enrollment may still require underwriting.
My take: treat this as a bet on your future health, not a hunt for the lowest monthly bill.
Final Thoughts
The cheapest premium today can become the most expensive choice tomorrow, and the six-month Medigap window at 65 is one deadline you really don't want to fumble.