Medicare's annual enrollment window runs through December 7, and roughly 34 million Americans in Medicare Advantage plans face a decision that can swing their out-of-pocket costs by thousands of dollars next year.
The choice between Medicare Advantage and Medicare Supplement plans isn't just about premiums.
It's about what happens when you actually get sick.
Medicare Advantage plans, run by private insurers, often advertise $0 monthly premiums and extras like dental, vision, and gym memberships.
The catch sits in the fine print: copays, coinsurance, prior authorizations, and annual out-of-pocket maximums that can reach $8,850 for in-network care in 2025, according to federal limits.
Medicare Supplement plans, also called Medigap, work differently.
You pay a monthly premium, but the plan picks up most of the costs traditional Medicare doesn't cover.
There are no networks, no referrals, and no prior authorization for covered services.
You can see any doctor in the country who accepts Medicare.
A Medigap Plan G for a 65-year-old can run $120 to $200 per month depending on the state, while a Medicare Advantage plan might cost $0 to $50.
Over a year, that's a difference of $1,500 or more before you ever see a doctor.
One hospital stay, a cancer diagnosis, or a specialist-heavy year can blow past the savings on premiums in a Medicare Advantage plan.
Medigap enrollees typically face far more predictable costs once the premium is paid.
A 2024 KFF analysis found that Medicare Advantage enrollees were more likely to report problems getting care, including denials that were later overturned on appeal.
Prior authorization requirements remain a flashpoint, with federal regulators tightening rules on how plans use algorithms to deny coverage.
Medicare Advantage plans must cover the same core benefits as traditional Medicare, and many offer extra perks that Medigap doesn't touch, like hearing aids and over-the-counter allowances.
For healthy seniors on tight budgets, the low premium can be the difference between affording coverage and going without.
The catch nobody mentions at the seminar: Medigap plans are hardest to buy after your initial enrollment window.
In most states, insurers can reject you or charge more based on health history once you're past that six-month period.
Switch from Advantage to Medigap later, and you may be locked out entirely.
That's why financial planners often tell clients to treat the first Medicare decision as a one-way door.
Choosing Medicare Advantage to save $150 a month now can mean losing the ability to buy Medigap at any price if a chronic condition shows up in five years.
New York and Connecticut require year-round guaranteed issue for Medigap, making switching easier.
If you live in Florida, Texas, or Arizona, the clock is ticking louder.
For anyone turning 65 or already enrolled, the practical move is to price both options with your actual doctors and prescriptions in hand.
Medicare's Plan Finder tool and the State Health Insurance Assistance Program offer free comparisons.
An independent broker who sells both types can show the real out-of-pocket math, not just the monthly premium.
The closing thought: the cheapest premium is rarely the cheapest plan.
Final Thoughts
Run your worst-case year, not your best-case one, before December 7 arrives.