HCC V28: The CMS-HCC Model V28 Explained
V28 is the most significant change to Medicare risk adjustment in years. This guide explains what the model is, why CMS introduced it, the transition timeline, and what it means for your RAF scores.
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Key data points
- V28 phase-in by payment year: 2024 = 67% V24 / 33% V28, 2025 = 33% / 67%, 2026 = 100% V28.
- Payment HCCs change from roughly 86 (V24) to about 115 (V28), with new, non-interchangeable numbering.
- Thousands of diagnosis codes that risk-adjusted under V24 carry no risk weight under V28.
Source: CMS CY2024 Medicare Advantage and Part D Rate Announcement.
Payment impact: because HCCs remap between models, a member can score differently under V28 than V24. The V24 vs V28 tool shows the dollar delta for a given profile, and what a RAF score is walks a full example.
What Is HCC V28?
The CMS-HCC model is the risk adjustment methodology that converts a patient's demographics and documented conditions into a RAF score. V28 is the latest version, finalized in the CY2024 Medicare Advantage Rate Announcement. It replaces the long-standing V24 model with an updated ICD-10-based clinical classification, a revised and expanded set of HCCs, and recalibrated coefficients.
Why CMS Introduced V28
CMS designed V28 to improve the accuracy and stability of risk adjustment: to recalibrate the model on more recent fee-for-service data, to reduce the influence of diagnosis codes that were susceptible to coding variation rather than true clinical difference, and to better align payment with predicted cost. The practical consequence is a model that rewards specific, well-documented chronic disease and de-emphasizes vaguely coded conditions.
The V24-to-V28 Phase-In Schedule
CMS blends the two models over three payment years rather than switching at once:
| Payment Year | V24 weight | V28 weight |
|---|---|---|
| 2024 | 67% | 33% |
| 2025 | 33% | 67% |
| 2026 | 0% | 100% |
During the blend years, a patient's effective RAF is a weighted average of the V24 and V28 results. The RAF V24 vs V28 comparison tool shows both scores and the blended figure side by side.
Key Changes in V28
- Updated clinical classification: the diagnosis-to-HCC mapping was rebuilt on the ICD-10 framework.
- Renumbered, expanded HCCs: categories grow from roughly 86 payment HCCs (V24) to about 115 (V28), with new numbering — old and new HCC numbers are not interchangeable.
- Fewer risk-bearing codes: thousands of ICD-10 codes that mapped to an HCC under V24 no longer carry risk weight under V28.
- Recalibrated coefficients: weights were re-estimated on more recent fee-for-service experience.
- Constrained coefficients: related conditions within a clinical group are constrained so severity is rewarded more consistently (see below).
At a glance — how the two models differ (confirm exact values against the current CMS Rate Announcement):
| Aspect | CMS-HCC V24 | CMS-HCC V28 |
|---|---|---|
| Payment HCCs | ~86 | ~115 (renumbered — not interchangeable) |
| Risk-bearing ICD-10 codes | More inclusive | Thousands fewer (narrower) |
| Documentation specificity | Lower bar | Higher — specificity matters more |
| Disease coefficients | V24 weights | Re-estimated on newer FFS data; many reweighted |
| Status in PY2026 | Retired for payment | 100% in effect |
| Classification basis | Legacy mapping (ICD-9-rooted, crosswalked) | Rebuilt natively on the ICD-10 framework |
| Coefficient treatment | Unconstrained within clinical groups | Constrained — related conditions in a group are limited |
Constrained Categories Explained
"Constraining" means CMS assigns the same coefficient to clinically related HCCs within a group so that the model does not over-reward differences that are driven by coding rather than true severity. For example, conditions within a related diabetes or heart-failure family may be constrained to a common weight. This reduces the payment swing between similar codes and pushes organizations toward accurate clinical documentation rather than code selection.
Impact on RAF Scores
Because V28 removes many codes from risk adjustment and constrains coefficients, many organizations see lower average RAF scores as the blend shifts toward V28. Conditions that were captured under V24 but dropped in V28 no longer contribute, and previously high-value codes may be constrained. The organizations least affected are those with accurate, specific, well-supported documentation of genuine chronic disease. To quantify the change for your population, run the same patients through the RAF Score Calculator under each model.
How to Prepare for V28
- Re-map high-volume conditions to their V28 HCCs using the ICD-10 to HCC crosswalk.
- Identify V24 codes that no longer risk-adjust in V28 and assess documentation quality for those patients.
- Model the financial impact of the blend across payment years 2024–2026.
- Strengthen documentation and education so capture reflects true clinical complexity — not code-level optimization.
Score patients under HCC V28 now
Enter ICD-10 codes to get an instant V28 RAF score with full HCC mapping and the V24/V28 blend.
Open the HCC V28 CalculatorFrequently Asked Questions
Version 28 of the CMS-HCC risk adjustment model. It updates the ICD-10-to-HCC mapping, renumbers and expands HCCs, removes many codes from risk adjustment, and recalibrates coefficients.
Phased over three payment years: 2024 = 67% V24 / 33% V28, 2025 = 33% V24 / 67% V28, 2026 = 100% V28.
Many organizations see lower average RAF scores because V28 drops codes from risk adjustment and constrains coefficients, raising the importance of specific documentation.
V24 uses ~86 payment HCCs; V28 expands and renumbers to ~115 HCCs, drops thousands of codes from risk adjustment, and recalibrates on more recent data. See the V24 vs V28 comparison.
This page is educational and does not constitute coding, billing, legal, or clinical advice. CMS-HCC V28 rules, code lists, and coefficients are defined by the official CMS Rate Announcement and may change by payment year; always confirm against current CMS guidance and your organization's compliance team. CPT® is a registered trademark of the American Medical Association; HEDIS® is a registered trademark of the National Committee for Quality Assurance (NCQA). This page is independent and is not affiliated with, endorsed by, or sponsored by CMS, the AMA, or NCQA.