V24 vs V28 HCC Models: Key Differences Explained

The CMS-HCC Model Transition

CMS is transitioning from the V24 risk adjustment model to the V28 model over a three-year phase-in period. In 2026, the blend is 33% V24 / 67% V28, moving to 100% V28 in 2027.

This transition significantly impacts which conditions are HCC-relevant and how much each condition contributes to the RAF score.

What Changed in V28

New HCC Categories Added

V28 introduced several new HCC categories that did not exist in V24:

HCC Categories Removed or Consolidated

V28 reduced the total number of HCC categories from 86 (in V24) to 115 distinct categories with different numbering. Many V24 categories were:

RAF Weight Changes

Every HCC coefficient was recalibrated in V28. Some conditions now carry higher weights, while others carry lower weights. This means:

Side-by-Side Comparison

Impact on Medical Coders

What coders need to do differently

1. Check both models — During the transition, verify that codes map correctly in both V24 and V28

2. Watch for dropped HCCs — Conditions that were HCC-relevant in V24 may not be in V28

3. Code to highest specificity — This was always important, but V28 makes it even more critical

4. Update reference materials — Any coding reference based solely on V24 is now incomplete

Tools that help

HCC Buddy displays HCC mapping for both V24 and V28 on every code lookup. This dual-model display ensures coders can see at a glance whether a code maps in one model, both, or neither.

Planning for 2027

By 2027, V24 will be fully retired. Organizations should:

Look up any code and see its V24 and V28 mapping side by side at hccbuddy.com/encoder.

Free resource: Download the HCC Coding Cheat Sheet — a printable V28 quick reference with the V24/V28 blend schedule, top HCC categories, and documentation tips.