If you're turning 65 or reviewing your coverage right now, you've probably stared at two options that sound similar but work nothing alike.
One caps your costs but locks you into a private network.
The other lets you see almost any doctor but comes with a monthly bill that never goes away.
Picking the wrong one can mean thousands of dollars in surprise charges, and in most states, you can't easily switch back.
Medicare Advantage, also called Part C, is run by private insurers.
You usually pay a low or $0 monthly premium, but you agree to use the plan's network of doctors and hospitals.
Copays for visits, labs, and hospital stays add up as you use care, and every plan sets an annual out-of-pocket maximum that caps your worst-case year.
Medicare Supplement plans, often called Medigap, work differently.
You keep original Medicare and buy a private policy that pays most of the gaps, like the 20% coinsurance on doctor visits and hospital costs.
Premiums run higher, often $100 to $250 a month depending on your state, age, and plan letter.
In exchange, your costs are far more predictable.
The catch that trips people up: Medigap has near-total freedom to see any provider who accepts Medicare, with no referrals and no network.
Advantage plans often throw in extras like dental, vision, hearing, and gym memberships, which look great on a brochure.
But those perks come with prior authorizations, provider networks, and denials that can delay care.
A 2024 KFF analysis found that a typical Medicare Advantage enrollee could face thousands in cost sharing for a serious health event, while many Medigap plans leave you with very little beyond the premium.
If you're healthy and rarely see a doctor, Advantage can be the cheaper route.
If you have chronic conditions, travel, or want to see specialists without approval, Medigap often wins.
The decision gets harder because of a rule most people learn too late.
In most states, Medigap insurers can deny you or charge more based on your health after your initial enrollment window closes.
That window is generally six months starting when you're 65 and enrolled in Part B.
Miss it, and a future diagnosis could make switching from Advantage to Medigap expensive or impossible.
A handful of states, including New York and Connecticut, offer more flexibility, but most don't.
First, list your doctors and medications, then check whether each Advantage plan in your ZIP code includes them.
Second, compare the annual out-of-pocket maximum, not just the premium.
Third, if you can afford it and value flexibility, seriously consider Medigap during your one guaranteed window.
And always check whether your hospital is in-network, because out-of-network bills can wreck a budget fast.
Shopping tools like Medicare's Plan Finder and your State Health Insurance Assistance Program offer free, unbiased help.
Don't rely on a sales call that only pitches one brand.
The bottom line: this isn't about which plan is "better." It's about which one fits your health, your doctors, and your bank account for the next decade, not just next year.
Final Thoughts
Choose fast, because the easy switching door closes sooner than most people expect.