Every fall, millions of Americans sit down with a stack of Medicare mail and try to pick between two options that sound almost identical.
One promises low monthly premiums and extras like dental and vision.
The other costs more upfront but claims to cover almost everything.
The gap between those pitches and what actually lands in your mailbox is where people get hurt.
Medicare Advantage, also called Part C, is run by private insurers paid by the federal government.
Premiums can be as low as zero dollars on top of your Part B fee, which is why the ads look so good.
The tradeoff is networks, prior authorizations, and copays that show up later.
A 2023 KFF analysis found that a small share of prior authorization requests get denied, but those denials cluster around expensive care.
Medicare Supplement plans, often called Medigap, work differently.
You pay a private insurer a monthly premium, and in exchange it picks up most of what original Medicare leaves behind.
There are no networks in the Advantage sense.
The catch is the price, which can run well past $150 a month depending on your age, state, and plan letter.
Here is the part that rarely makes the commercial.
Medigap is easiest to buy during your six-month Medigap Open Enrollment Period, which starts when you are 65 and enrolled in Part B.
Outside that window, most states let insurers check your health history and charge you more or refuse you outright.
Switch from Advantage to Medigap later, and you may find the door locked.
Advantage plans can be changed every year during open enrollment, and you can usually move between them without underwriting.
Medigap does not offer that flexibility in most states.
So the choice at 65 is not a one-year decision.
It is closer to a one-way valve for many people.
Advantage plans often include drug coverage and caps on out-of-pocket spending, which helps people with modest savings.
Medigap plus a separate Part D drug plan can cost meaningfully more each month but leaves fewer surprises when you actually get sick.
The right answer depends on your health, your doctors, and how much cash you can absorb in a bad year.
Some brokers earn higher commissions on one product than the other, and that can shape the advice you get.
Check whether your doctors are in a specific Advantage network before you enroll, not after.
If you are turning 65, the calendar matters more than the brochure.
Missing your Medigap window can cost you for decades.
The system is not rigged against you on purpose, but it is not built to explain itself either.
Read the summary of benefits, call your doctors, and price both paths before you sign.
Final Thoughts
The cheapest premium is rarely the cheapest year.