When you turn 65, Medicare hands you a decision that quietly determines thousands of dollars of your retirement budget.
The fork in the road: Medicare Advantage (Part C) or a Medicare Supplement plan (Medigap).
Both replace or fill gaps in Original Medicare, but they work in completely opposite ways — and picking wrong can leave you stuck.
The price tags look wildly different upfront.
Medicare Advantage plans advertised on TV often show $0 premiums, plus extras like dental, vision, and gym memberships.
Medigap plans can run $100 to $200 a month or more, depending on your state and age, with no freebies attached.
That gap is why Advantage now covers more than half of all eligible Medicare beneficiaries, according to federal data.
The catch is what happens after the premium.
Advantage plans work like an HMO or PPO: you stay in a network, get prior authorization for many services, and pay copays as you go.
There's an annual out-of-pocket maximum — in 2025, in-network caps run as high as $9,350 for some plans.
A rough year with a hospital stay, cancer treatment, or a skilled nursing stay can push you toward that ceiling fast.
You pay a higher monthly premium, but the plan picks up most of what Original Medicare doesn't — coinsurance, copays, deductibles, and no network restrictions.
You can see any provider who accepts Medicare nationwide, and there's no prior authorization for covered care.
A serious illness might cost you almost nothing beyond the premium.
The trap most people miss is the switching window.
Medigap insurers in most states can reject you or charge more based on health history once you're past your six-month Medigap Open Enrollment Period, which starts when you're 65 and enrolled in Part B.
Get diagnosed with diabetes, heart disease, or cancer after that window, and affordable Medigap may be off the table permanently.
Advantage plans, by contrast, accept nearly everyone during annual enrollment.
If you start with a cheap Advantage plan and develop a costly condition, you may be financially locked in.
If you start with Medigap, you keep the option to downgrade to Advantage later — though you'd lose the premium you paid.
Most Advantage plans bundle Part D prescription coverage.
Standalone Medigap does not, so you'll buy a separate Part D plan and pay its premium.
Advantage plans also change their networks, formularies, and copays every single year — your plan today isn't guaranteed to look the same next January.
The practical answer depends on three things: your health, your tolerance for risk, and your cash flow.
Someone with chronic conditions and the budget for premiums often comes out ahead with Medigap.
Someone healthy, cost-conscious, and willing to work within a network may do fine with Advantage — as long as they understand the ceiling.
Before you decide, check whether your doctors accept the specific plan, add up the worst-case annual cost for each option, and confirm your state's Medigap rules.
A handful of states, including New York and Connecticut, allow year-round switching with fewer health questions, which changes the calculus entirely. **The bottom line:** The $0 premium isn't free — it's a trade.
You're swapping predictable monthly costs for unpredictable ones later, and that bet gets harder to unwind every year you wait.
Final Thoughts
Run the worst-case numbers before you sign, not after the hospital bill arrives.