Medicare's annual enrollment window closes December 7, and the choice between Medicare Advantage and a Medicare Supplement plan is the single most expensive decision most seniors will make this year.
The two paths look similar on a brochure but work in completely opposite ways once the bills arrive.
Medicare Advantage, also called Part C, replaces Original Medicare with a private plan.
Premiums often start near $0, and many plans bundle in dental, vision, hearing, and drug coverage.
The trade-off is networks: you generally must stay in-network, and referrals are common for specialists.
Medicare Supplement plans, known as Medigap, work differently.
You keep Original Medicare and buy a private policy that covers most of the gaps, including the 20% coinsurance that has no annual cap under basic Medicare.
You can see any provider nationwide who accepts Medicare, with no referrals in most cases.
The premium gap is where the math gets real.
A Medigap Plan G for a 65-year-old can run $100 to $160 a month in many states, on top of the standard Part B premium, which is $185 in 2025.
Advantage plans often cost $0 to $50 monthly, so the savings look obvious up front.
Advantage plans cap your yearly out-of-pocket costs, but those caps can reach $9,350 for in-network care in 2025, and higher if you go out of network.
A Medigap Plan G deductible is $257 in 2025, and after that, most covered care is paid.
If you sign up during your six-month Medigap Open Enrollment Period, which starts when you're 65 and enrolled in Part B, insurers generally can't turn you down or charge more because of health history.
Wait too long, and you may face medical underwriting, price hikes, or a denial.
That rule is why advisors often tell healthier seniors to grab Medigap first, even at a higher monthly cost, then switch to Advantage later if premiums climb.
Going the other direction is far harder because underwriting can block you.
Formularies shift, networks shrink, and a plan that covered your cardiologist in 2024 may not in 2025.
You should check your doctors and prescriptions against next year's plan before the deadline, not after.
Both paths now run through Part D, and the 2025 redesign caps out-of-pocket drug spending at $2,000.
That cap softens the blow for expensive prescriptions, but only if the plan actually covers your specific medication.
If you travel a lot or split time between states, Medigap's nationwide access is hard to beat.
If you rarely see doctors and want the lowest monthly bill, Advantage can work, as long as you can absorb a surprise hospital stay.
Missing the December 7 deadline can leave you without drug coverage, trigger late penalties, and lock you out of your one guaranteed shot at Medigap.
My take: treat this as a bet on your future health, not your current checkbook.
Final Thoughts
The cheapest premium today can become the most expensive plan tomorrow, and the one window to buy Medigap without answering health questions closes fast.