Turning 65 comes with a paperwork pile most people never see coming.
And buried in that pile is one decision that can swing your health care costs by thousands of dollars a year: Medicare Advantage or a Medigap supplement.
Original Medicare pays about 80% of covered costs, leaving you on the hook for the rest with no cap.
A Medigap supplement plugs that hole, usually for a predictable monthly premium.
Medicare Advantage instead hands your coverage to a private insurer that bundles hospital, doctor, and often drug coverage into one plan — frequently with a $0 premium but copays and networks attached.
The premium math is where people get tripped up.
A Medigap Plan G might run $120 to $180 a month depending on your state and age, on top of the standard Part B premium.
That sounds steep next to a $0-premium Advantage plan.
But Advantage plans can charge up to $9,350 in out-of-pocket costs for in-network care in 2025, and more if you go out of network.
Two hospital stays could wipe out the savings from a decade of premiums.
Advantage plans often include extras like dental, vision, hearing, and gym memberships.
Medigap plans don't — but they let you see any provider in the country who accepts Medicare, with no referrals and no prior authorization for most care.
If you travel, snowbird, or have a specialist you trust, that flexibility matters.
When you first enroll in Medicare, you get a six-month window to buy any Medigap policy regardless of your health history.
Miss it, and insurers in most states can reject you or charge more based on conditions like diabetes, heart disease, or cancer.
Switching from Advantage back to Medigap later is often expensive or impossible.
Advantage plans do have an escape hatch: you can try one and switch back to Original Medicare during the annual enrollment window each fall.
But you can't always add a supplement at that point.
That asymmetry — easy to leave, hard to return — is the single most important thing to understand before you pick.
If you're healthy, rarely see doctors, and want low upfront costs, an Advantage plan can work well.
If you have ongoing conditions, travel, or simply want to know your worst-case number, a supplement buys predictability.
Picking without running your own prescriptions and doctors through each plan's network is.
Before you decide, check two things: whether your doctors and hospitals are in the Advantage plan's network, and what your specific drugs cost under each option.
Medicare's Plan Finder tool does this in about 20 minutes.
A local SHIP counselor will do it with you for free.
Our take: the $0 premium is the most expensive marketing trick in American health care.
It's not free — you're just paying with uncertainty instead of a check.
Final Thoughts
Run your real numbers, not the brochure's.