E66.01
BillableMorbid (severe) obesity due to excess calories
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is E66.01 an HCC code?
Yes. E66.01 maps to Morbid Obesity under the CMS-HCC V28 risk adjustment model (and Morbid Obesity under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for E66.01
For E66.01 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed E66.01 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
E66.01 is the ICD-10-CM diagnosis code for morbid (severe) obesity due to excess calories. Severe obesity caused by consuming too many calories, significantly impacting health and requiring medical intervention. E66.01 sits in the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89), within the section covering overweight, obesity and other hyperalimentation (e65-e68).
Under the CMS-HCC V28 risk adjustment model, E66.01 maps to Morbid Obesity (HCC 48) with a community, non-dual, aged base RAF weight of 0.226. Under the older V24 model, E66.01 mapped to the same category but with a base RAF weight of 0.250 — V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This is a more specific code than general obesity; use when morbid obesity is documented. Because E66.01 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for E66.01 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a more specific code than general obesity; use when morbid obesity is documented
- •Morbid obesity typically refers to BMI ≥40 or ≥35 with comorbidities
Clinical Significance
Morbid (severe) obesity due to excess calories represents a chronic metabolic disease with a body mass index of 40 or greater, or 35 or greater with serious obesity-related comorbidities. This condition significantly increases the risk of type 2 diabetes, cardiovascular disease, obstructive sleep apnea, osteoarthritis, and certain cancers. It requires comprehensive medical management and may qualify the patient for bariatric surgical intervention.
Documentation Requirements
- ✓Documentation must include a specific body mass index value (typically 40 or above, or 35 or above with comorbidities), the provider's explicit diagnosis of morbid or severe obesity, and identification of excess caloric intake as the etiology.
- ✓Associated comorbid conditions (diabetes, hypertension, sleep apnea, osteoarthritis) should be listed and linked to obesity when applicable.
- ✓A Z68.4x body mass index code should be assigned additionally.
- ✓Current treatment plan including dietary, exercise, pharmacological, and surgical considerations should be documented.
Excludes 1 — Do NOT code together
- morbid (severe) obesity with alveolar hypoventilation (E66.2)
Commonly Confused Codes
- •E66.09 (Other obesity due to excess calories) captures non-morbid obesity.
- •E66.2 (Morbid obesity with alveolar hypoventilation) specifically includes Pickwickian syndrome and should not be confused.
- •E66.813 (Obesity, class 3) is an alternative code for severe obesity based on body mass index classification.
- •E66.1 (Drug-induced obesity) identifies medication-related weight gain.
- •Z68.4x (Body mass index 40 and over) is an additional code, not a replacement.