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Annual enrollment for 2027 Medicare Advantage is open right now, through December 7, and the headline number from the Centers for Medicare and Medicaid Services sounds encouraging: CMS projects an average Medicare Advantage premium of $12 a month for 2027, down 16.5% from $14.37 in 2026. Before anyone treats that as good news, it is worth understanding how the math works.

The average fell because expensive plans were removed from the pool, not because insurers got more generous. The two largest Medicare Advantage insurers, UnitedHealth Group and Humana, are exiting more counties than they are entering in 2027. UnitedHealth Group is exiting 228 counties and entering just 9, and Humana is exiting 62 counties and entering 4. A KFF analysis finds 193 counties will have no Medicare Advantage drug plan for general enrollment in 2027, up from 123 last year. Fewer plans, concentrated in markets where carriers can still turn a profit, pull the average down arithmetically.

The coverage losses are real at the member level. About 600,000 people are in a Humana Medicare Advantage plan that is ending in 2027, as Humana’s CFO said on the company’s second-quarter 2026 earnings call. That is on the order of 8% of Humana’s roughly 7 million Medicare Advantage members. UnitedHealth and Humana together account for at least 75% of Medicare Advantage enrollment in 28% of U.S. counties, so when one withdraws from a rural market, there is often no comparable replacement.

Why are they leaving? Carriers are prioritizing profitability over footprint. Medical costs have risen, and Medicare Advantage payment updates have not been enough, in insurers’ view, to keep margins intact everywhere. On top of that, contracts rated 4 stars and above earn bonus payments that lower-rated ones do not, so insurers have a strong incentive to concentrate on their better-performing contracts and drop the rest. Analysts also note that payers are increasing cost-sharing for enrollees, narrowing networks, and cutting supplemental benefits after a spike in utilization and medical costs over the last couple of years.

The premium figure obscures a second problem hiding in the plan data. Premiums fell 16.5% nationally, from $14.37 to $12.00, but other forms of cost exposure can still rise even as premiums fall. In particular, out-of-pocket maximums and drug cost-sharing vary widely by plan and county, and many enrollees will see higher cost sharing in 2027 even if the sticker premium looks lower.

For investors, the relevant question is where the pain lands and who absorbs it. UnitedHealth Group (UNH) and Humana (HUM) are voluntarily shrinking to protect margins rather than absorbing losses at scale. Humana’s CFO described the strategy as using plan exits to prioritize higher-performing plans. CVS Health’s Aetna (CVS) is following a similar path, with standard plans pulled from 123 counties and exits from Maryland and New Hampshire. Hospital operators like HCA Healthcare (HCA) face a related pressure: as Medicare Advantage plan availability contracts in some markets and members shift plans, reimbursement rates and the revenue mix for large health systems can change.

The revenue pressure on hospital systems runs deeper than Medicare Advantage alone. HCA Healthcare’s results show what happens to hospital economics when insurance coverage unravels at scale.

Cigna (CI) has limited Medicare Advantage exposure after its prior exits and sits somewhat apart from this cycle, but the broader managed-care sector is reassessing the risk of underwriting Medicare at scale, and that recalibration is not finished.

The enrollment period closes December 7. Anyone currently in a plan being discontinued should have received a notice and may qualify for a special enrollment period. Even if your premium looks stable, check your Annual Notice of Change for network and benefit changes before assuming continuity. The $12 average belongs to someone else’s plan in someone else’s county. Your actual cost depends entirely on what is still available where you live.

The enduring lesson here applies well beyond Medicare: a falling average conceals enormous dispersion. When large players exit a market, the index improves while the people left behind face fewer choices, not better ones. Always look past the headline figure to the underlying structure it is measuring.