Complete Guide to HCC V28 Changes for 2026

Introduction to CMS-HCC Version 28

The CMS-HCC Version 28 model represents the most significant overhaul to the Medicare Advantage risk adjustment system in over a decade, with the official software and ICD-10 mapping files published by CMS. For medical coders working in risk adjustment, understanding these changes is not optional, it directly affects which diagnosis codes carry financial weight, how conditions are grouped, and what documentation strategies your organization needs to prioritize.

CMS introduced V28 as a phased transition beginning with Payment Year 2024 and reaching full implementation in Payment Year 2026. During the 2024 to 2025 transition, the legacy V24 model and the new V28 model ran simultaneously and the final Risk Adjustment Factor score was a weighted blend (PY2025 was 33% V24 / 67% V28). Payment Year 2026 is the first year scored on 100% V28, so the blend no longer applies.

If you are new to HCC coding, start with our introduction to HCC coding for foundational concepts before diving into the V28 changes below.

Timeline: The V24 to V28 Transition

CMS chose a phased approach to give health plans, providers, and coders time to adapt. The transition schedule is as follows:

What does "blend" mean in practice? Both models are run independently using the same set of submitted diagnosis codes. Each model produces its own Risk Adjustment Factor score. The final score is then calculated as a weighted average. For example, if a patient's V24 Risk Adjustment Factor score is 1.200 and their V28 score is 1.050, the last blend year was Payment Year 2025: (0.33 x 1.200) + (0.67 x 1.050) = 0.396 + 0.704 = 1.100. For Payment Year 2026 onward there is no blend, the score is simply the V28 score of 1.050.

This blending means that during the transition period, coders need to understand both models. A code that mapped to an HCC in V24 but not in V28 carried partial value during the 2024 to 2025 blend, but in 2026 (100% V28) it carries no Risk Adjustment Factor value at all. For a deeper comparison between the two models, see our V24 vs V28 guide.

What Changed in V28: The Big Picture

The structural changes between V24 and V28 are substantial. Here is a high-level summary:

The net effect is a model that is more clinically precise but also more demanding of documentation specificity and coding accuracy.

New HCC Categories in V28

V28 introduced several new and restructured HCC categories. These reflect CMS's effort to better capture conditions that drive significant healthcare costs:

CMS added these categories because their cost prediction models showed these conditions were being inadequately captured or grouped under categories that did not reflect their true cost impact.

Deleted or Consolidated HCC Categories

Equally important for coders to understand are the categories that were removed or consolidated in V28:

The practical impact for coders is clear: some conditions that reliably generated Risk Adjustment Factor value under V24 no longer do so under V28. Organizations that relied on capturing unspecified diabetes or other previously-qualifying conditions will see Risk Adjustment Factor erosion unless they adapt their documentation and coding strategies.

Key ICD-10-CM Mapping Changes

Beyond the structural HCC changes, the actual code-to-category mappings shifted in important ways:

Codes that lost their HCC mapping (critical for coders to know):

Codes that gained new or different HCC mappings:

Through the 2024 to 2025 transition you had to check both models, because a code with no V28 HCC could still carry value under the V24 portion of the blend. For 2026 dates of service (100% V28) that is no longer true, though the V24 mapping still matters for prior-year and RADV review. You can search any ICD-10 code at hccbuddy.com/encoder to see both V24 and V28 HCC mappings side by side.

Risk Adjustment Factor Weight Changes

Even for HCC categories that exist in both V24 and V28, the Risk Adjustment Factor weights changed, sometimes dramatically:

Higher weights in V28 (more Risk Adjustment Factor value):

Lower weights in V28 (less Risk Adjustment Factor value):

To compare V24 and V28 weights for any specific HCC, use HCC Buddy's Risk Adjustment Factor Calculator which displays coefficients for both models.

What This Means for Medical Coders

The V28 changes create several imperatives for coders working in risk adjustment:

Specificity matters more than ever. The trend in V28 is unmistakable, unspecified codes increasingly map to lower-value HCCs or no HCC at all. Coders must query providers for specificity when documentation is ambiguous. "Diabetes" is not enough; "diabetes with diabetic chronic kidney disease" is what captures HCC 37.

Documentation improvement is a coding function, not just a clinical one. Coders should be actively participating in clinical documentation improvement programs, flagging charts where specificity gaps result in lost HCC capture. The gap between what a provider knows about a patient and what the documentation supports has financial consequences under V28 that are larger than under V24.

Both models must be checked during the blend period. A code that appears to have no value under V28 may still contribute Risk Adjustment Factor value through the V24 portion of the blend. Conversely, a code that maps to a new V28 HCC might not have had value under V24. Coders need tools that display both mappings simultaneously.

Audit scrutiny will intensify. CMS Risk Adjustment Data Validation audits will review coding accuracy under both models during the blend period. Overcoding under either model creates audit exposure.

How HCC Buddy Helps with V28

HCC Buddy was built for exactly this transition. Every code lookup shows both V24 and V28 HCC mappings side by side, so coders can spot mapping differences between models:

Search any ICD-10 code at hccbuddy.com/encoder to see its V28 HCC mapping instantly, or try the Risk Adjustment Factor calculator to model the blend impact on your patient population.

Conclusion

CMS-HCC V28 is not an incremental update, it is a fundamental restructuring of how diagnosis codes translate to risk adjustment value. With 115 categories replacing the old 86, new disease groupings, deleted legacy categories, and recalibrated weights, coders who understand V28 will be significantly more effective than those still working from V24 assumptions.

The key takeaways for 2026:

Start using HCC Buddy, sign up for Pro. See both V24 and V28 mappings for every code, every time.

Free resource: Download the HCC Coding Cheat Sheet, a printable V28 quick reference with top HCC categories, common non-HCC codes, and documentation tips.