If you're turning 65 or reviewing your coverage this fall, you're about to face one of the most expensive decisions of your retirement.
It comes down to two very different paths: Medicare Advantage or Original Medicare with a Medigap supplement.
Pick wrong, and the gap can run into thousands of dollars a year.
Medicare Advantage, also called Part C, is the all-in-one option.
Private insurers bundle your hospital, doctor, and drug coverage, often throwing in dental, vision, and gym memberships.
The pitch is easy: many plans carry a $0 monthly premium, and the average enrollee pays far less per month than someone on Original Medicare.
Advantage plans come with networks, prior authorizations, and copays that can stack up fast.
A 2024 KFF analysis found that nearly half of Advantage enrollees who needed costly care still faced cost-sharing, and out-of-pocket maximums can reach $8,850 for in-network care before the plan pays everything.
You pay a standard Part B premium, and then you choose any doctor in the country who accepts Medicare.
There are no networks and no prior authorization for most services.
But without a supplement, you're on the hook for 20% of most outpatient costs with no ceiling.
That's why most people pair it with a Medigap plan.
A Plan G policy can run $130 to $300 a month depending on your age, health, and state.
Add a Part D drug plan, and a healthy 65-year-old might pay $250 or more monthly before seeing a single doctor.
In return, Medigap picks up nearly everything Medicare doesn't, and you can see any participating provider nationwide.
The real dividing line is flexibility versus predictability.
Advantage caps your monthly cost and offers extras, but limits who you see and how fast you get care approved.
Medigap costs more upfront but turns unpredictable medical bills into a known monthly number.
There's one rule that trips up a lot of people.
If you choose Advantage when you first enroll and later want to switch to Medigap, insurers in most states can charge you more or deny you outright based on your health.
Your one guaranteed window to buy Medigap without underwriting is usually the six months after you first enroll in Part B.
Miss it, and a new diagnosis like diabetes or heart disease can lock you out of the best plans.
Some states, including Connecticut, Massachusetts, Maine, and New York, offer easier switching rules.
That single fact makes the initial choice far more consequential than the monthly premium suggests.
If you have chronic conditions, travel often, or want to keep your current doctors, Medigap tends to pay off even at a higher monthly cost.
If you're generally healthy, live near a strong local network, and want to keep premiums low, Advantage can work well, as long as you understand the trade-offs.
The worst move is picking on premium alone and reading the details later.
Run your own numbers, check whether your doctors and hospitals are in-network, and look up the plan's out-of-pocket maximum.
A few hours of homework now beats a surprise bill later.
Our take: treat this like buying insurance, not shopping for a deal.
The cheapest monthly plan is rarely the cheapest year, and the decision you make at 65 is hard to undo.
Final Thoughts
Read the fine print before the deadline, not after the first claim is denied.