If you are turning 65 or reviewing your coverage right now, there is a decision sitting in front of you that most people get wrong the first time.
It is not about which insurance company has the friendliest commercials.
It is about two very different ways to plug the holes in original Medicare, and the gap between them can run into the thousands of dollars every year.
On one side you have Medicare Advantage, often called Part C.
These are private plans that bundle hospital, medical, and usually drug coverage into one monthly premium that can look shockingly low, sometimes near zero dollars.
On the other side you have Medicare supplements, also known as Medigap, which charge a real monthly premium but pick up most of the copays, coinsurance, and deductibles that original Medicare leaves behind.
The catch with Advantage plans is not the premium.
It is what happens when you actually use the coverage.
Every plan sets its own copays for doctor visits, hospital stays, and specialist care, and you can face prior authorizations before treatment is approved.
In a bad year, a hospital stay or a cancer diagnosis can mean thousands in out-of-pocket costs, even though the monthly bill looked tiny.
Once you pay your Part B premium and the supplement premium, most plans cover their share of approved care with no network restrictions.
You can see any doctor in the country who accepts Medicare.
That freedom is the reason a Plan G or Plan N can run $120 to $200 or more per month depending on your age, gender, and state.
Medigap plans are the most forgiving when you first enroll.
During your initial six-month window, insurers generally must sell you a policy regardless of your health history.
Wait too long, or switch to Advantage and try to come back later, and you can be denied or charged more because of conditions like diabetes, heart disease, or cancer.
Advantage plans, by contrast, must accept you every year during open enrollment, no matter your health.
That asymmetry is why financial planners often tell healthy people to think hard before trading a supplement for a lower premium.
You may save now and pay later, when you can least afford it.
Advantage plans usually include Part D, while Medigap does not, so you would buy a separate drug plan.
Those standalone plans are cheap, but Advantage drug formularies can change every January, and the medications you take today may not be covered the same way next year.
First, add up your realistic worst-case year, not your best-case one.
Look at the plan's maximum out-of-pocket limit and compare it to twelve months of supplement premiums.
Second, check whether your doctors and hospital are in the Advantage network.
Third, if you have any chronic condition, treat the ability to switch back to a supplement later as something you may not get.
There is no universal winner here, and anyone selling you a one-size answer is selling something else too.
But the people who end up frustrated are usually the ones who picked on premium alone and never read the copay list.
My take: run the math on a bad year, not a good one, and protect your right to change your mind while you still have it.
Final Thoughts
A low premium feels great until the first hospital bill arrives.