Medicare open enrollment opens today and runs through December 7. The headline numbers favor Medicare Advantage by a wide margin — and that is precisely why the decision deserves more care than the premium comparison suggests.
The 2027 Numbers Are Genuinely Attractive
CMS released its 2027 projections on September 28, 2026. The weighted average monthly Medicare Advantage premium is expected to fall from $14.37 to $12.00, a 16.5% decline. For MA plans that include drug coverage, the average monthly Part D premium — after rebates are applied — drops from $11.32 to $7.00, a 38% cut.
Compare that to standing still in Original Medicare with a stand-alone drug plan, where the average Part D premium edges up from $35.09 to $36.00.
Plan availability is holding steady: 5,532 MA plans nationally for 2027, versus 5,553 this year. More than 99% of beneficiaries have access to at least one MA plan, 97% can choose among ten or more, and CMS says roughly eight in ten current MA enrollees can stay in their existing plan at the same or a lower premium. The agency projects 34 million MA enrollees in 2027 — 47.4% of all Medicare enrollment.
The Part Nobody Prices In
Switching from Original Medicare into Medicare Advantage is easy and reversible on paper: you can move back during any annual open enrollment. What is not guaranteed is the Medigap supplement policy that makes Original Medicare financially workable — the coverage that pays the 20% coinsurance Part B leaves open-ended.
Your federally protected window to buy any Medigap policy sold in your state, at the best available rate and regardless of health, is the six-month period beginning the first month you are both 65 or older and enrolled in Part B. Outside that window and a short list of guaranteed-issue situations, Medicare.gov states the position plainly: "there's no federal guarantee that an insurance company will sell you a Medigap policy. If you're able to buy one, it may cost more due to past or present health problems."
There is a trial right. If Medicare Advantage was your first Medicare choice when you became eligible — or you dropped a Medigap policy to try MA for the first time — you have 12 months to return to Original Medicare with guaranteed Medigap rights, and you must apply in the window running from 60 days before to 63 days after your MA coverage ends. Miss it and the protection is gone.
Only four states — Connecticut, Massachusetts, Maine, and New York — require continuous or annual guaranteed issue regardless of medical history. KFF finds just 10% of MA enrollees age 65 and older live in them.
The exposure is not theoretical. KFF's analysis of 2023 encounter data found 74% of full-year Medicare Advantage enrollees — about 20.9 million people — had a condition that could trigger a Medigap denial. That share rises to 88% at age 85 and up, and reaches 82% in Florida.
Practical Takeaways
- Treat the choice as structural, not annual. A $12 premium is a one-year number; underwriting risk compounds with age and diagnosis.
- Know which window you are in. If you are newly eligible, your six-month Medigap window is the most valuable enrollment right you will ever hold. If you joined MA within the past year, confirm whether your trial right is still live.
- Check your state's rules before assuming you can switch back; four states protect you, the rest largely do not.
- Model the worst year, not the average one. MA plans cap out-of-pocket spending; Original Medicare without Medigap does not.
Sources: CMS, "Medicare Advantage and Medicare Prescription Drug Programs Expected to Remain Stable in 2027" (September 28, 2026); Medicare.gov, "When can I buy a Medigap policy?" and Medigap guaranteed issue rights; KFF, "Nearly Three-Quarters of Medicare Advantage Enrollees Could be Denied a Medigap Policy Due to a Pre-Existing Condition"; KFF, "Medigap Enrollment and Consumer Protections Vary Across States."