If you're turning 65 or reviewing your coverage right now, there's one decision that quietly shapes your healthcare budget for years: Medicare Advantage or a Medicare Supplement plan.
Both replace the gaps in original Medicare, but they work in opposite ways, and picking wrong can mean thousands in surprise costs.
Medicare Advantage, also called Part C, is the all-in-one route.
Private insurers bundle hospital, medical, and usually drug coverage into one plan, often with a $0 premium on top of the standard Part B charge.
You generally stay in-network, need referrals for specialists, and face copays for visits, scans, and hospital stays.
Every plan sets its own rules, and those rules can change each year.
A Medicare Supplement plan, sometimes called Medigap, works differently.
You keep original Medicare and add a private policy that pays most of what Medicare doesn't, such as the 20% coinsurance and hospital deductibles.
You can see any provider nationwide who accepts Medicare, no referrals, no network.
The catch is the premium, which often runs $100 to $250 a month depending on your age, plan letter, and state.
The money math is where people get tripped up.
Advantage plans look cheap because the premium is low or zero.
But out-of-pocket maximums can reach $8,850 in 2026 for in-network care, and higher if you go out of network.
A rough year with a hospital stay, a few specialists, and imaging can wipe out the savings fast.
Medigap charges more monthly but caps your exposure, which makes budgeting predictable.
Medigap does not, so you'll buy a separate drug plan.
If you take expensive medications, compare formularies and copays carefully.
A plan that looks affordable can sting at the pharmacy counter.
There's also a timing rule that can't be undone.
When you first enroll in Part B at 65, you get a six-month Medigap open enrollment window.
During that time, insurers can't charge you more or deny you because of health conditions.
Miss it, and you may face medical underwriting later.
That's the single biggest reason financial planners tell people to decide early.
If you're healthy, want low premiums, and don't mind networks, Advantage can work well.
If you travel, see multiple specialists, or want predictable costs, Medigap often wins.
The honest answer is that it depends on your doctors, your prescriptions, and how much surprise you can absorb.
Check your current providers against each plan's network.
Add up premiums plus worst-case out-of-pocket costs, not just the monthly number.
And if you're still inside that first Medigap window, treat it like a deadline, because it is one.
The bottom line: the cheapest premium is rarely the cheapest plan.
Final Thoughts
Run the numbers for a bad year, not just a good one, and you'll usually see which option protects your wallet.