If you're turning 65 this year, your mailbox is probably stuffed with promises of $0 premiums, free dental, and cash back on groceries.
Those ads are for Medicare Advantage plans.
The alternative, a Medicare Supplement (often called Medigap), rarely advertises because it doesn't need to.
The two paths work completely differently, and picking the wrong one can cost you thousands a year.
Here's the plain-English breakdown. **Medicare Advantage (Part C)** replaces Original Medicare with a private plan.
You usually pay a low or $0 monthly premium, but you agree to the insurer's network of doctors and hospitals.
Copays show up for visits, labs, and hospital stays.
Many plans include extras like dental, vision, and gym memberships.
In 2025, Advantage plans can charge up to $9,350 in in-network out-of-pocket costs before coverage kicks in fully.
That's real money if you end up with a hospital stay or a cancer diagnosis. **Medigap** works the opposite way.
You keep Original Medicare and add a supplement that covers most of what Medicare doesn't, including deductibles and coinsurance.
There are no networks, so you can see any doctor in the country who takes Medicare.
Medigap can run $100 to $250 or more per month depending on your age, health, and state.
On top of that, you still pay the standard Part B premium, which is $185 a month in 2025.
So the math comes down to this: Advantage is cheap monthly and expensive when you get sick.
Medigap is expensive monthly and cheap when you get sick.
There's one deadline that matters more than any other.
When you first enroll in Medicare Part B, you get a six-month Medigap open enrollment window.
During that time, insurers must sell you any policy at standard rates, no matter your health history.
Miss that window and you can be denied or charged more for a pre-existing condition like diabetes, heart disease, or cancer.
In most states, that window never reopens.
This is the single biggest reason financial planners tell healthy 65-year-olds to at least consider Medigap now rather than later.
Advantage plans, by contrast, let you switch every year during open enrollment from October 15 to December 7.
That flexibility sounds great, but it cuts both ways.
Insurers also change their networks and formularies every year, and a doctor you love can drop out of your plan with little notice.
One more thing people miss: if you pick Advantage and later want Medigap, you may have to pass medical underwriting.
A few states, including New York and Connecticut, offer year-round guaranteed enrollment, but most don't.
If you're healthy, take few prescriptions, and want the lowest monthly cost, Advantage can work well.
If you have chronic conditions, travel a lot, or simply want predictable costs, Medigap tends to win over the long run. **Our take:** Treat this as a 20-year decision, not a monthly bill.
Saving $150 a month now can evaporate fast after one serious hospital stay, and the window to buy Medigap without answering health questions closes sooner than most people realize.
Final Thoughts
Talk to a licensed broker who sells both types before you check a box.