CMS-HCC V24 vs V28: A Side-by-Side Comparison for Risk Adjustment Teams

Why This Comparison Matters

The CMS-HCC V24 vs V28 comparison reveals fundamental structural changes that affect every risk adjustment workflow. 2026 is the first year operating under 100% CMS-HCC V28, completing a transition that began with blended weights in 2024 (67% V24, 33% V28) and continued in 2025 (33% V24, 67% V28). For risk adjustment teams, understanding exactly what changed between the models is not an academic exercise; it directly determines revenue strategy, coding priorities, and operational focus.

Many organizations adapted to V28 incrementally during the transition, making gradual adjustments as the V28 weighting increased. That approach was reasonable during blended years, but 2026 demands a complete shift. Teams still operating with V24 mental models, whether in coding practices, provider education materials, or analytical assumptions, will systematically underperform.

• Revenue Recalibration: Every revenue projection, bid assumption, and financial model must be rebuilt using V28 coefficients. V24-based revenue estimates are no longer directionally useful.
• Coding Priority Realignment: Conditions that were high-value under V24 may carry different or no value under V28. Coding and documentation efforts must be redirected to conditions that matter under the current model.
• Operational Retooling: Scoring engines, gap analysis algorithms, and reporting tools must use V28 logic exclusively. Any system still referencing V24 mappings or coefficients produces incorrect outputs.

This comparison provides risk adjustment teams with a structured reference for understanding the differences that matter most to their day-to-day operations. For the complete RAF score fundamentals, start with our comprehensive guide.

Structural Differences

The structural architecture of V28 differs from V24 at every level, from the number of categories to how they are organized and how the model was calibrated.

• HCC Count: V24 contained 86 HCCs organized into 24 condition groups. V28 contains 115 HCCs organized into 26 disease families. The increase in HCCs reflects V28's greater granularity in distinguishing clinical conditions, not an expansion of conditions that generate revenue.
• Model Basis: V24 was calibrated using ICD-9 era data and crosswalked to ICD-10. V28 was calibrated directly on ICD-10 encounter data from 2017-2019, eliminating the artifacts and approximations inherent in the V24 crosswalk approach.
• Disease Family Structure: V28 reorganized condition categories into 26 disease families that better reflect clinical relationships. Some conditions that were grouped together under V24 are separated in V28, while others that were separate are now combined. This restructuring affects hierarchy application and interaction factors.
• Demographic Segments: Both models segment by community versus institutional setting and by Medicaid dual-eligibility status. V28 recalibrated all demographic coefficients, meaning the base value for a given age-sex-eligibility combination differs between models even before any HCCs are applied.
• Interaction Factors: V28 modified the disease interaction terms that generate additional risk weight when certain condition combinations are present. Some V24 interactions were eliminated, others were modified, and new interactions were added reflecting the updated clinical evidence base.
• Normalization Factor: The normalization factor that adjusts RAF scores for budget neutrality differs between models, meaning a raw score of 1.5 under V24 and 1.5 under V28 do not represent the same predicted cost.

HCC and Code Mapping Changes

The changes to ICD-10 to HCC mapping are where V28 creates the most operational impact for coding and documentation teams.

• Net Code Reduction: V24 mapped 9,797 ICD-10 codes to HCCs. V28 maps 7,770 codes, a net reduction of 2,027. This means 2,294 codes that previously generated HCCs no longer do, while 268 new codes were added. Organizations must identify which removed codes affect their populations.
• Specificity Requirements: V28 eliminated many unspecified codes that mapped to HCCs under V24. Conditions must now be documented and coded with greater specificity to map. For example, unspecified diabetes codes that generated HCCs under V24 require type, complication, and body system specification under V28.
• New HCC Categories: V28 introduced new HCCs that did not exist in V24, including separate categories for conditions like pressure ulcers by stage, certain cancers by location, and substance use disorders by substance type. These new categories create capture opportunities that V24 did not support.
• Eliminated HCC Categories: Some V24 HCCs were removed entirely from V28, meaning conditions that previously contributed to RAF scores no longer do regardless of how they are coded. Plans must identify which eliminated categories affected their historical revenue and adjust projections accordingly.
• Remapped Conditions: Some ICD-10 codes that mapped to one HCC under V24 now map to a different HCC under V28, changing which hierarchy applies and which coefficient is assigned. This remapping can increase or decrease the value of specific diagnoses depending on the new HCC assignment.

The practical impact: coding teams must update their V28 mapping references and recalculate RAF scores for every member using V28 logic. V24 scoring outputs are no longer valid for any operational purpose.

Coefficient and Constraining Differences

Constraining is the single most impactful change in V28 and the one that risk adjustment teams find most difficult to internalize because it contradicts a fundamental V24 assumption.

• V24 Approach: Under V24, each HCC carried a unique coefficient reflecting its predicted cost impact. More severe conditions within a disease group carried higher coefficients. Diabetes with renal complications was worth more than diabetes without complications because the coefficient was larger.
• V28 Constraining: Under V28, related HCCs within the same disease family are constrained to carry identical coefficients regardless of severity. All diabetes HCCs except pancreas transplant now share the same coefficient of approximately 0.166. Whether a patient has uncomplicated diabetes or diabetes with multiple severe complications, the risk adjustment value is the same.
• Revenue Impact of Constraining: For plans with populations concentrated in severe manifestations of chronic diseases, constraining significantly reduces RAF scores. A patient with V24 HCC 18 (Diabetes with Chronic Complications, coefficient approximately 0.368) now receives the same V28 coefficient as uncomplicated diabetes (approximately 0.166), a 55% reduction in condition value.
• Conditions Most Affected: Disease families with the widest coefficient ranges under V24 experience the largest constraining impact. Diabetes, cardiovascular disease, and renal conditions, which had significant spread between severity levels under V24, show the most compression under V28.
• Strategic Implications: Under V24, plans could optimize revenue by ensuring the most severe manifestation of each condition was captured. Under V28, the severity level within a constrained family does not affect the RAF score. This shifts coding priority from severity capture to comprehensive condition capture across all disease families.

Beyond constraining, V28 recalibrated all coefficients based on updated cost data. Even conditions not subject to constraining carry different coefficients than their V24 equivalents. Plans must use current V28 coefficient tables for all revenue calculations, not adjusted V24 values.

Condition-by-Condition Impact

The following disease categories represent the areas of greatest divergence between V24 and V28, where risk adjustment teams should focus their operational attention.

• Diabetes: Under V24, diabetes HCCs ranged from 0.105 (without complications) to 0.368 (with chronic complications). Under V28, all diabetes HCCs are constrained to approximately 0.166. Plans with high diabetes severity see the largest revenue reduction. Coding focus shifts from severity documentation to ensuring every diabetic comorbidity is captured as an independent HCC in its own disease family.
• Heart Failure: V28 restructured heart failure into new HCC categories with different mapping logic. Some heart failure codes that generated high-value HCCs under V24 map to lower-value or different categories under V28. Coding specificity for ejection fraction and heart failure type becomes more important.
• Chronic Kidney Disease: V28 modified renal disease categories and their interaction with diabetes. CKD stages that previously generated independent HCC value may now be constrained within the renal disease family. The diabetes-CKD interaction factor was also recalibrated.
• Mental Health and Substance Use: V28 expanded coverage of behavioral health conditions with new HCC categories for specific substance use disorders and psychiatric conditions that were not separately recognized under V24. This creates new capture opportunities for plans with significant behavioral health populations.
• Cancer: V28 restructured cancer HCCs with greater specificity by location and type. Some cancers that shared a single HCC under V24 are now separated into distinct categories. Coding accuracy for cancer site and histology becomes more important for correct HCC assignment.
• Vascular Disease: Peripheral vascular disease, cerebrovascular disease, and related conditions were reorganized with modified hierarchy logic. Conditions that were hierarchically related under V24 may now be independent under V28, creating additional capture opportunity.

For a complete analysis of V28 changes, see our detailed guide to CMS-HCC V28.

What Teams Should Do Now

With V28 as the sole model, risk adjustment teams should take the following actions to ensure their operations are fully aligned with the current model.

• Audit All Scoring Systems: Verify that every tool, calculator, and scoring engine used in your organization runs V28 logic exclusively. Check API integrations, spreadsheet-based tools, vendor platforms, and internal analytics systems. Any system still referencing V24 coefficients or mappings must be updated immediately.
• Retrain Coding Staff: Provide V28-specific training that covers changed mappings, eliminated codes, new HCC categories, and the practical implications of constraining. Focus training on the specific disease categories most prevalent in your population.
• Update Provider Education: Refresh all provider-facing documentation improvement materials to reflect V28 priorities. Emphasize condition capture breadth over severity depth, and update documentation templates to prompt for V28-specific coding requirements.
• Recalculate Revenue Projections: Rerun all revenue models using V28 coefficients. Compare against actual year-to-date performance to identify whether your plan is tracking above or below V28-adjusted expectations. Use this analysis to inform second-half coding and documentation priorities.
• Identify New Capture Opportunities: Review the 268 newly mapped codes and new HCC categories in V28 to identify conditions that were not previously revenue-generating but now are. These represent net-new capture opportunities that did not exist under V24.
• Rebuild Benchmarks: Historical RAF benchmarks based on V24 or blended years are no longer valid baselines. Establish new V28-native benchmarks using 2026 data and current coding standards as the reference point for ongoing performance measurement.