2026 MA Enrollment Surprises: SNP Growth Rewrites 2027 Bid Math

Medicare Advantage enrollment grew by 1.1 million people to reach 51.6% penetration in 2026, against the decline carriers' own bid submissions had projected to CMS. Special needs plans absorbed 85% of that net increase, up from 48% of net growth in 2025.

The headline penetration figure moved a point. The membership mix underneath it moved considerably further, and the risk model pricing 2027 was calibrated on neither.

Key Takeaways

• 85% of net growth came from SNPs, against 48% a year earlier. Individual non-SNP growth of 224,000 members was the slowest in any year between 2007 and 2025.
• 45% year-over-year growth in chronic-condition C-SNPs added roughly 518,000 members and lifted C-SNPs to 20% of the SNP population, while C-SNP plan offerings rose 46% from 376 to 548.
• V28 reached full weight for payment year 2026 on a calibration built from 2018 FFS diagnoses and 2019 FFS expenditures. CMS declined to finalize the proposed 2023-2024 recalibration for 2027.
• A 3-point spread separates the V24-to-V28 risk score effect for full duals (-2.3%) from non-duals (+0.7%), concentrated in the population that still makes up 78% of SNP enrollment.
• $76 billion is MedPAC's estimate of 2026 MA payments above what traditional Medicare would have spent, with $28 billion attributed to coding intensity and a further $57 billion to favorable selection.

What Plans Projected and What Enrolled

Every June, MA organizations file the following year's bids with CMS, and those bids embed the plan's own enrollment projection. For 2026 the aggregate signal was retrenchment: CMS advance guidance drawn from plan submissions projected enrollment falling to 34 million from 34.9 million, with MA's share of Medicare dropping to 48% from 50%. CMS hedged its own figure at publication, saying it anticipated enrollment "will be more robust than the plans' projections".

It was. KFF reported 35 million enrollees by February 2026, a 3% year-over-year gain, and Arnold Ventures put the final figure at 51.6% penetration on 1.1 million net new members.

The denominator needs stating before that number travels. KFF frames MA enrollment against beneficiaries it defines as MA-eligible, arriving at 55%, or 35.2 million of 64.2 million. Arnold Ventures frames it against the full Medicare population and arrives at 51.6%. Both are correct and they answer different questions, so a penetration assumption pulled into a bid model needs its denominator confirmed before it is compared with an internal figure.

Underneath the topline, SNP enrollment reached 8.2 million beneficiaries, 23% of total MA enrollment against 21% a year earlier. Within it, D-SNPs fell to 78% of SNP enrollment from 83% while C-SNPs surged to 20% on 45% growth, roughly 518,000 members. Institutional SNPs added about 9,000 and stayed flat at 2%.

2026 MA Enrollment and Offering Growth by Segment

Segment	2025	2026	Change
SNP share of MA enrollment	21%	23%	+2 pts, 8.2M members
SNP share of net MA growth	48%	85%	+37 pts
C-SNP plan offerings	376	548	+46%
D-SNP plan offerings	909	1,019	+12%
Non-SNP individual plan growth	n/a	+224K members	Slowest since 2007
Group MA enrollment	n/a	Down 40K members	First decline since 2010

Supply confirms the demand was not accidental. SNP offerings rose 19% nationally, from 1,445 to 1,721 plans, with C-SNP offerings up 46% from 376 to 548 while I-SNP offerings contracted 4%. Non-SNP offerings moved the other way, down 9% from 3,719 to 3,373, and employer group MA enrollment declined by roughly 40,000, its first drop since 2010.

V28 Prices a Population It Was Not Calibrated On

The CMS-HCC V28 risk adjustment model reached full weight for payment year 2026, closing a three-year phase-in begun in 2024. It is calibrated on 2018 Medicare fee-for-service diagnoses and 2019 FFS expenditures, a general Original Medicare population rather than one weighted toward the dual-eligible and chronic-condition beneficiaries now driving MA's growth.

CMS proposed updating that calibration to 2023 diagnoses and 2024 expenditures for 2027. Combined with normalization the revision would have cut MA payments by 3.32%. CMS declined to finalize it, keeping the 2018-2019 calibration and applying a smaller 1.12% normalization reduction instead. The model pricing 2027 payments is therefore two enrollment cycles removed from the population it scores, and the gap widened in the direction SNP growth predicts.

MedPAC's March 2026 report sizes the aggregate distortion: MA payments in 2026 ran $76 billion above what traditional Medicare would have spent on the same beneficiaries, $28 billion of it from coding intensity, with MA risk scores about 4% higher than comparable FFS beneficiaries after V28's full implementation, down from 10% in 2022. Favorable selection adds a further $57 billion. Both figures blend the whole MA population, which is the problem for a book moving compositionally faster than an aggregate can register.

A 2023 SNP Alliance survey conducted by Milliman found the V24-to-V28 risk score effect was not uniform by dual status. The median plan-level change was -2.3% for full duals and -2.8% for partial duals, against +0.7% for non-duals. That 3-point spread lands squarely on the segment still making up 78% of SNP enrollment, so a plan whose 2026 membership skewed more dual than its 2025 book absorbed more of V28's compression than the MedPAC aggregate implies.

The revenue mechanics compound it. Risk-adjusted revenue is the bid multiplied by the realized risk score of the enrolled population, and a newly enrolled member's first-year score is systematically suppressed relative to true condition burden until documentation, typically an Annual Wellness Visit, catches up at the new plan. For a book that absorbed hundreds of thousands of new C-SNP enrollees in 2026, the score currently being earned understates morbidity, and the correction arrives in 2027 looking like trend acceleration rather than coding catch-up.

The Yardstick Is Moving Too

At 51.6% penetration, or 55% on KFF's eligible-beneficiary denominator, MA passed a threshold that changes what the comparison population means.

Actuarial models built when MA represented 40% to 45% of Medicare, as recently as 2020, were calibrated against a program where a meaningful share of relatively healthy beneficiaries remained in traditional Medicare by choice. That is the dynamic feeding the $57 billion of favorable selection MedPAC still estimates. As MA share climbs past the midpoint, the residual FFS population that anchors V28's own reference calibration, and that MedPAC benchmarks MA payments against, is itself shrinking and skewing toward beneficiaries who did not or could not choose MA.

That is a reflexivity problem distinct from the composition mismatch. The yardstick is drifting at the same time the thing being measured is growing to dominate the program, and neither the V28 calibration nor the FFS benchmark population has been refreshed past 2019 expenditure data.

A countervailing force sits inside the SNP book itself. Milliman documents a decline in D-SNP value-added benefits, driven by supplemental benefit and OTC allowance cuts, which could slow D-SNP enrollment growth even as C-SNP growth continues. That would push the mix further toward the C-SNP segment where plan tenure is shortest, claims history thinnest, and the coding-intensity benchmark least applicable. Rose Mollitor of ATI Advisory put the top line at "just under a 1% increase in overall enrollment" while describing a "refocusing of the large carriers" underneath it, which is the part a penetration trendline does not carry.