HCC V28 Overview for Coders
A plain-English overview of the CMS-HCC version 28 risk adjustment model, how ICD-10-CM codes map to HCCs, the phase-in from V24, and why coding rules stay the same.
On this page
Short answer
HCCs (Hierarchical Condition Categories) group ICD-10-CM diagnosis codes for risk adjustment in Medicare Advantage. CMS phased in the 2024 CMS-HCC model, known as V28, from payment year 2024, fully replacing V24 by payment year 2026. V28 changed which diagnosis codes map to payment HCCs and how the categories are grouped, but it did not change the ICD-10-CM Official Guidelines - codes are still assigned only from provider documentation.
Key takeaways
- HCCs are groupings of diagnosis codes used to predict expected costs in risk-adjusted payment models.
- CMS phased in V28 over three payment years: 2024, 2025 and 2026, with V28 fully in place for 2026.
- Some codes that mapped to a payment HCC under V24 no longer do under V28, and some new mappings were added.
- Risk adjustment never changes how a code is chosen. Code what is documented, following the Official Guidelines.
Risk adjustment uses diagnosis codes to estimate how much care a patient population is likely to need. In Medicare Advantage, CMS does this with the CMS-HCC model, and the current version is known as V28. This page explains how HCCs relate to ICD-10-CM codes and what changed with V28.
What an HCC is
A Hierarchical Condition Category (HCC) is a group of ICD-10-CM diagnosis codes that are clinically related and expected to have similar costs. The model:
- Maps each reported diagnosis code to zero or one HCC.
- Applies hierarchies: when a patient has codes in several related HCCs, only the most severe one counts.
- Combines the HCCs with demographic factors to produce a risk score.
Most ICD-10-CM codes do not map to a payment HCC at all. Those that do tend to describe chronic or serious conditions.
What changed with V28
The 2024 CMS-HCC model (V28) was a significant revision of the earlier V24 model:
- The HCCs were reorganized and renumbered, with updated clinical groupings and hierarchies.
- The set of ICD-10-CM codes that map to payment HCCs changed: some codes that counted under V24 no longer map to a payment HCC, and some mappings were added.
- The model was recalibrated on more recent data.
The phase-in
CMS phased V28 in over three payment years by blending risk scores from the two models:
Check the CMS announcement for the exact blend percentages and model details for the payment year you are working on.
What did not change: the coding rules
Risk adjustment uses the codes that are reported; it does not change how they are chosen.
- Codes are assigned from provider documentation, following the ICD-10-CM conventions and the Official Guidelines for Coding and Reporting.
- A condition must be documented in the record for the encounter to be coded. Many organizations use documentation frameworks such as MEAT (monitor, evaluate, assess, treat) to check that support exists; MEAT is an industry practice rather than a CMS rule.
- Coders and CDI specialists should never add or select a code because it maps to an HCC. Ask a compliant, non-leading query when the documentation is unclear.
How ICD Code Finder helps
- Code pages show an HCC V28 badge for codes that map to a payment HCC in the mapping loaded with the code set, so you can see at a glance which diagnoses carry risk-adjustment weight.
- The Query Builder drafts non-leading provider queries when documentation is incomplete. Drafts must be reviewed before they are sent.
Always confirm HCC mappings against the official CMS mapping files for the payment year in question.
Frequently asked questions
What does HCC stand for?
Hierarchical Condition Category. HCCs group related ICD-10-CM diagnosis codes into categories, and hierarchies make sure only the most severe category in a related group counts for a patient.
When did V28 fully replace V24?
Do I code differently because of HCCs?
No. ICD-10-CM codes must be assigned from provider documentation according to the Official Guidelines, regardless of whether a code maps to an HCC. Coding a condition to affect risk scores without supporting documentation is not acceptable.
Does ICD Code Finder show HCCs?
Code pages show an HCC V28 badge when the code maps to a payment HCC in the mapping loaded with the code set. Always confirm against the CMS mapping for the payment year you are working on.
Informational, not coding advice. This page summarizes ICD-10-CM conventions for education. Always code from the medical record using the current ICD-10-CM Tabular List, Alphabetic Index and Official Guidelines for Coding and Reporting, plus payer policy.
Look up ICD-10-CM codes free.
Search the current code set with instructional notes, Excludes1/Excludes2, 7th characters and GEMs, then build and check code sets.