Monday brought some unpleasant news for health insurers. The Centers for Medicare & Medicaid Services dropped its annual Medicare Advantage payment proposal for 2027, and let's just say the numbers weren't what Wall Street had in mind. Instead of the comfortable 4% to 6% rate increase analysts were expecting, CMS proposed a net average payment bump of just 0.09%. Yes, you read that correctly. Less than one-tenth of one percent.

That translates to about $700 million in additional payments to Medicare Advantage plans, which sounds substantial until you realize it's spread across the entire industry and represents essentially flat growth. The market's reaction was swift and brutal.

The Fallout Hits Major Insurers

By Tuesday morning, health insurance stocks were in full retreat. UnitedHealth Group Inc. (UNH) plunged 13.13% to $305.48 in premarket trading. Humana Inc. (HUM) dropped 15.03% to $224.00. CVS Health Corporation (CVS) slid 11.41% to $74.30. Alignment Healthcare, Inc. (ALHC) fell 15.20% to $20.19.

The pain spread across the sector. Centene Corporation (CNC) dropped 7.28% to $42.91. Elevance Health, Inc. (ELV) fell 7.14% to $350.00. Even Molina Healthcare Inc. (MOH) was down 6.04% at $188.91, according to Benzinga Pro data.

Why the Numbers Came In So Low

The disconnect between Wall Street expectations and reality comes down to one key assumption: the growth rate of traditional Medicare spending. Federal actuaries used a 4.97% growth estimate for traditional Medicare costs, which directly influences how much the government pays Medicare Advantage plans. Analysts had expected that number to be higher, and historically, actuaries sometimes revise these estimates as new data comes in before finalizing rates in April.

But for now, that lower spending growth assumption is what's driving the anemic proposed increase. When you factor in estimated risk score trends tied to coding practices and population changes, the average expected payment change rises to 2.54%, but that's still well below what the Street was modeling.

The agency calls this the Effective Growth Rate, and it's a fundamental component in setting benchmarks for Medicare Advantage payments. It reflects projected growth in Original Medicare per capita costs as estimated by the Office of the Actuary.

What CMS Says It's Trying to Accomplish

CMS Administrator Mehmet Oz framed the proposal as a matter of fiscal responsibility and program integrity. "These proposed payment policies are about making sure Medicare Advantage works better for the people it serves," Oz said Monday. "By strengthening payment accuracy and modernizing risk adjustment, CMS is helping ensure beneficiaries continue to have affordable plan choices and reliable benefits, while protecting taxpayers from unnecessary spending that is not oriented towards addressing real health needs."

Translation: The agency wants to make sure it's paying for actual health needs, not inflated risk scores or administrative gamesmanship. CMS emphasized three guiding principles for its approach: reducing administrative burden through simplicity, enabling fair competition among plans, and ensuring payments accurately reflect beneficiary health risk.

The Technical Changes Under the Hood

Beyond the headline rate, CMS proposed some meaningful updates to how it calculates risk adjustment for Part C. The agency wants to continue using version 28 of the clinical classification system but recalibrate it with more recent Original Medicare data, updating diagnoses and expenditure years to better reflect current costs.

One notable change: CMS proposed excluding diagnoses from audio-only encounters and from unlinked chart review records starting in 2027, though plans would still be allowed to submit those records. This is part of the broader push toward payment accuracy and away from what the agency apparently views as less reliable documentation methods.

For Program of All-Inclusive Care for the Elderly organizations, CMS reiterated its plan to transition risk adjustment fully to the encounter data system. For 2027, the agency proposed blending risk scores evenly between the 2017 CMS-HCC model and the proposed 2027 model as part of a phased transition.

The agency noted that policies affecting Puerto Rico would largely continue existing approaches to support stability in a market where Medicare Advantage enrollment is significantly higher than in other jurisdictions.

Part D and Star Ratings

On the prescription drug side, CMS proposed risk adjustment updates reflecting changes from the Inflation Reduction Act and more recent data, while also refining predictive accuracy for prescription drug plans. The Advance Notice also detailed proposed updates and feedback requests related to Part C and Part D Star Ratings, though substantive changes to those ratings would be subject to future rulemaking.

This is all part of the required annual process CMS uses to update payment rates and refine technical assumptions. The Calendar Year 2027 Advance Notice of Methodological Changes for Medicare Advantage capitation rates and Part C and Part D payment policies is now out for comment, with final rates expected in April.

For health insurers banking on robust Medicare Advantage growth to drive their business models, Monday's proposal was a cold splash of reality. Whether these rates hold or get revised upward as more data comes in remains to be seen, but for now, the market is pricing in the possibility that the gravy train might be slowing down.