If you're turning 65 this year, you've probably already been buried in mailers promising free dental, free groceries, and a $0 monthly premium.
Those offers come from Medicare Advantage plans, and they look like a steal next to the alternative.
The alternative is a Medicare Supplement plan, often called Medigap.
It doesn't cover groceries or gym memberships.
What it does is pick up most of the leftover costs that original Medicare doesn't pay, and that difference is where the real money hides. **The monthly premium is the wrong number to look at** Medicare Advantage plans often advertise a $0 premium because the government pays private insurers a set amount per member.
In exchange, you agree to use the plan's network and its rules, including prior authorizations for many procedures and services.
You pay a monthly premium that can run $100 to $200 or more depending on your state, age, and plan letter.
In return, you can see any provider in the country who accepts Medicare, and you generally don't need referrals or approvals.
That trade-off matters most the year something goes wrong.
A hospital stay, a cancer diagnosis, or a specialist referral can push Advantage enrollees into copays that add up fast. **The out-of-pocket cap isn't the safety net it sounds like** Advantage plans do cap your yearly out-of-pocket spending, but those caps can sit around $8,000 or more for in-network care.
Some plans set separate, higher limits for out-of-network care, and many services require approval before they're covered at all.
Medigap Plan G, one of the most popular options, leaves you with only the Part B deductible, which runs just over $250 in 2025.
After that, most covered care is handled.
There's no network, no prior authorization for covered services, and no surprise bill after a procedure.
The catch is that Medigap doesn't include drug coverage.
You'll need a separate Part D plan, which adds another premium, usually somewhere between $0 and $50 a month depending on the plan. **Where the Advantage pitch gets expensive** Advantage plans often include extras that Medigap can't touch: dental cleanings, hearing aids, over-the-counter allowances, and sometimes a grocery card.
For a healthy 65-year-old on a tight budget, those perks are real and immediate.
Insurers can change their networks and formularies every year, and a drug or doctor that's covered in January may not be covered the following January.
You can switch plans during open enrollment, but switching from Advantage back to Medigap later is the part that trips people up.
In most states, Medigap insurers can reject you or charge more based on your health once you're past your initial enrollment window.
A diagnosis that shows up in your late 60s can lock you into Advantage whether you want it or not. **A simple way to think about it** If you can afford the Medigap premium and you want predictable costs and full provider access, Medigap tends to be the safer long-term bet.
If the premium is out of reach or you'd rather keep the money now and accept the network rules, Advantage can work, especially if you're healthy and your doctors are already in-network.
Either way, check whether your hospitals and specialists are actually in the plan, read the formulary for your prescriptions, and look at the out-of-pocket maximum, not the premium. **Our take:** The $0 premium is not free money, it's a trade.
You're handing over flexibility and predictability in exchange for lower monthly costs, and that bet pays off for some people and backfires for others.
Final Thoughts
Run the numbers for a bad year, not a good one, before you sign.