Medicare's open enrollment window gets all the attention, but a quieter decision is costing some retirees hundreds of dollars a month.
It comes down to two very different paths: Medicare Advantage or a Medigap supplement.
Pick wrong, and you could be stuck with bills you never saw coming.
Medicare Advantage, often called Part C, bundles hospital, medical, and usually drug coverage into one plan run by a private insurer.
Many versions carry a $0 premium beyond what you already pay for Part B.
But the trade-off is a network of doctors, prior authorizations, and copays that can add up fast when you actually get sick.
Medigap, by contrast, works alongside Original Medicare.
You pay a monthly premium, often $100 to $200 or more depending on your state and age, and in exchange the plan covers most of the gaps—coinsurance, deductibles, and hospital costs.
You can see any provider in the country who takes Medicare.
If you sign up during your six-month Medigap open enrollment period, which starts the month you're 65 and enrolled in Part B, insurers generally can't turn you down or charge more because of your health.
Miss that window, and you may face medical underwriting.
A single diagnosis can mean a denial or a premium that stings.
Medicare Advantage has its own rule worth knowing.
You can switch plans or drop back to Original Medicare during the annual enrollment period from October 15 to December 7.
But if you want a Medigap policy after your trial right ends, the same underwriting problem returns in most states.
If you're healthy and rarely see a doctor, a $0-premium Advantage plan can look like a clear win.
If you have chronic conditions, travel a lot, or want to see specialists without referrals, the predictability of Medigap often pays for itself.
It's less about which is cheaper on paper and more about which fits your actual medical life.
One more thing trips people up: Advantage plans often include extras like dental, vision, and gym memberships.
Those perks are real, but they're not the reason to choose a plan.
Read the summary of benefits and the drug formulary before you're swayed by freebies.
A few states—including New York, Connecticut, Massachusetts, and Maine—have rules that make it easier to buy Medigap later or switch plans year-round.
If you live elsewhere, the timing decision matters even more.
My take: treat this like a budget question, not a brand loyalty question.
Add up your premiums, your likely copays, and the worst-case year, then compare.
Final Thoughts
The cheapest monthly plan isn't always the cheapest plan overall—and the most expensive one isn't automatically the safest.