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. 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 expected to reach full implementation by Payment Year 2027. During the transition, both the legacy V24 model and the new V28 model run simultaneously, with the final Risk Adjustment Factor score calculated as a weighted blend of both models. For Payment Year 2026, that blend is 33% V24 and 67% V28, meaning V28 now carries the dominant share of the calculation.

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:

Payment Year 2024: 67% V24 / 33% V28 — V24 still dominant, V28 introduced at one-third weight

Payment Year 2025: 50% V24 / 50% V28 — equal weighting, both models carry the same influence

Payment Year 2026: 33% V24 / 67% V28 — V28 now dominant, V24 influence winding down

Payment Year 2027: Expected 100% V28 — full transition complete, V24 retired

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 Payment Year 2026 blended score would be: (0.33 x 1.200) + (0.67 x 1.050) = 0.396 + 0.704 = 1.100.

This blending means that during the transition period, coders need to understand both models. A code that maps to an HCC in V24 but not in V28 still carries some Risk Adjustment Factor value in 2026 — just 33% of what it used to. 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:

V24 had 86 HCC categories; V28 has 115 HCC categories — a net increase of 29 categories, reflecting more granular clinical groupings

Many conditions were reclassified, split, or consolidated — conditions that shared a single HCC in V24 may now be separated into distinct categories with different weights

New categories added for substance use disorders, pressure ulcer staging, and more specific cancer classifications

Some conditions that were HCC-relevant in V24 are no longer HCC-relevant in V28 — the most notable being diabetes without complications

Risk Adjustment Factor weights were recalibrated across all categories — reflecting updated cost data and actuarial analysis

New disease interaction terms were added to account for the compounding effect of certain condition combinations

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 entirely new HCC categories that did not exist in V24. These reflect CMS's effort to better capture conditions that drive significant healthcare costs:

HCC 135: Substance Use Disorder, Moderate/Severe — Alcohol, opioid, and other substance dependence codes now map to a dedicated HCC, reflecting the high cost burden of substance use treatment. Only dependence codes (F1x.2-) qualify, not "use" codes (F1x.1-).

HCC 136: Substance Use Disorder, Mild — A lower-severity companion category for less severe substance use conditions.

HCC 381-384: Pressure Ulcer Categories — Pressure ulcers were reclassified with stage-specific HCCs. Stage 3 and Stage 4 pressure ulcers now map to higher-weighted categories, reflecting their intensive treatment costs.

HCC 263: Stem Cell Transplant — A new category recognizing the high cost of stem cell and bone marrow transplant patients.

HCC 267-268: Refined Cancer Staging — More granular cancer categories that differentiate between metastatic, active, and maintenance phases of cancer treatment.

HCC 328: Morbid Obesity — E66.01 now maps to its own dedicated HCC in V28, separate from other metabolic conditions.

HCC 238: Specified Heart Arrhythmias — Atrial fibrillation and other significant arrhythmias received their own category rather than being grouped with broader cardiac conditions.

HCC 329: Chronic Kidney Disease, Stage 3 — Stage 3 Chronic Kidney Disease received its own HCC separate from Stages 4 and 5, which map to HCC 326.

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:

V24 HCC 23: Diabetes without Complication — This is arguably the most impactful deletion. In V24, E11.9 (Type 2 diabetes mellitus without complications) mapped to HCC 19 and carried a Risk Adjustment Factor weight. In V28, diabetes without complications still maps to HCC 38, but the weight structure changed significantly. Coders must now capture specific complications to maximize appropriate risk adjustment.

V24 HCC 48: Morbid Obesity — Consolidated and remapped into the V28 structure as HCC 328 with different coding requirements.

V24 HCC 23 and 24: Diabetes Acute/Chronic Split — In V24, diabetes had three tiers (acute complications, chronic complications, without complications). V28 consolidated into two primary categories: HCC 37 (with chronic complications) and HCC 38 (without chronic complications or with other/unspecified complications).

Several lower-impact V24 HCCs were absorbed into broader V28 categories or eliminated when actuarial data showed they were not independently predictive of costs.

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):

E11.9 (Type 2 diabetes mellitus without complications) — Mapped to HCC 19 in V24; maps to a lower-weighted HCC 38 in V28

I10 (Essential hypertension) — Never mapped to an HCC in either model, but coders often confuse it with hypertensive heart disease codes that do map

I25.10 (Atherosclerotic heart disease of native coronary artery without angina pectoris) — Check carefully, as the HCC assignment changed between models

Multiple unspecified codes across disease categories lost their mappings as CMS pushed toward specificity requirements

Codes that gained new or different HCC mappings:

F10.20, F11.20, F12.20 (Alcohol, opioid, cannabis dependence, uncomplicated) — New HCC mapping in V28 under the substance use disorder categories

L89.x codes (Pressure ulcers by stage) — Remapped to the new stage-specific pressure ulcer HCCs

E66.01 (Morbid obesity due to excess calories) — Maps to the new HCC 328

During the blend period, it is essential to check both models for every code you are evaluating. A code that appears to have "no HCC" might still carry value under the V24 portion of the blend. 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):

Severe and advanced cancers saw weight increases, reflecting their intensive treatment costs

Organ failure categories (heart failure, respiratory failure, renal failure) generally received higher weights

Substance use disorders, as newly created categories, added entirely new Risk Adjustment Factor value that did not exist before

Stage 4 pressure ulcers received among the highest weights in the model

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

Some common chronic conditions saw weight reductions as CMS recalibrated to more recent cost data

Conditions that were previously grouped with higher-cost conditions and then separated into their own category may have lower individual weights

Diabetes categories saw weight restructuring, with the non-complicated category carrying less weight

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 simultaneously, so you never miss a mapping difference between models:

Dual-model display — Search any ICD-10-CM code and see the V24 HCC, V28 HCC, and both Risk Adjustment Factor weights on one screen

72,000+ codes indexed — The complete ICD-10-CM code set with HCC mappings for both V24 and V28 models

Risk Adjustment Factor calculator — Input patient demographics and HCC codes, compare V24 vs V28 scores, understand the blend impact

AI coding assistant — Ask natural language questions about V28 changes and get answers grounded in official CMS mapping data

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:

V28 is now the dominant model at 67% weight in the blend — treat it as your primary reference

Specificity is the single most important coding practice — unspecified codes lose value in V28

Check both models during the blend period to capture the full Risk Adjustment Factor picture

Use tools built for the transition — manual lookups across two models are slow and error-prone

Start using HCC Buddy — sign up for a 14-day Pro trial with no credit card required. 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.

Complete Guide to HCC V28 Changes for 2026