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E66.01 ICD-10-CM Code: Morbid (severe) obesity due to excess calories

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FY 2026 Apr update / Endocrine, nutritional and metabolic diseases (E00-E89) / Overweight, obesity and other hyperalimentation (E65-E68)

E66.01

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Morbid (severe) obesity due to excess calories

Severe obesity caused by consuming too many calories, significantly impacting health and requiring medical intervention.

Buddy the Bee presenting code insight

Buddy Insight

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.

CMS-HCC V28

HCC 48

RAF 0.186

CMS-HCC V24

HCC 22

RAF 0.250

ACA/HHS

N/A

—

Not mapped

ESRD/PACE

HCC 22

RAF 0.081

RXHCC

N/A

—

Not mapped

Code Book Path

Official
E66Overweight and obesity
E66.0Obesity due to excess calories
E66.01Morbid (severe) obesity due to excess calories

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for E66.01 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for E66.01 in this effective period.

Related Child Codes

Official
E66.09Other obesity due to excess calories

Includes

Official

ICD-10-CM does not list Includes notes for E66.01 in this effective period.

Excludes 1

Official
  • morbid (severe) obesity with alveolar hypoventilation (E66.2)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E66.01 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E66.01 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E66.01 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
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.

MEAT Support

HCC Buddy guidance
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.

Audit Caution

HCC Buddy guidance
Always assign an additional Z68.x body mass index code to document the specific value.
Do not assign both E66.01 and E66.813 for the same patient, as they represent overlapping severity.
Ensure the provider documents morbid or severe obesity specifically rather than just obesity.
Do not assume morbid obesity from a high body mass index alone without a provider diagnosis statement.

Common Mistakes

HCC Buddy guidance
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.

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is E66.01 an HCC code?

Yes. E66.01 (Morbid (severe) obesity due to excess calories) maps to Morbid Obesity under the CMS-HCC V28 risk adjustment model (and Morbid Obesity under V24), with a community non-dual aged RAF of 0.186. It is billable for payment year 2026.

Coder answer: E66.01 is billable and maps to V28 HCC 48, Morbid Obesity. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
E66.01
Description
Morbid (severe) obesity due to excess calories
HCC (V28)
HCC 48 — Morbid Obesity
RAF
0.186
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 48, Morbid Obesity
0.186
V24HCC 22, Morbid Obesity
0.250
ESRDHCC 22, Morbid Obesity
0.081

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. 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.

Work E66.01 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

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.

Coder workflow notes

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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 0.186. 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.

Morbid (severe) obesity due to excess calories, requires BMI >= 40 (or >= 35 with comorbidities) plus provider documentation of morbid obesity. Always pair with a Z68.* BMI code per 'use additional code' convention. 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

  • •Morbid (severe) obesity due to excess calories, requires BMI >= 40 (or >= 35 with comorbidities) plus provider documentation of morbid obesity. Always pair with a Z68.* BMI code per 'use additional code' convention.
  • •E66.01 is specifically for morbid obesity from excess caloric intake. If obesity is drug-induced (E66.1), post-surgical, or Cushing-related, the etiology code differs.
  • •V28 HCC 48 (Morbid Obesity) at RAF 0.186. Morbid obesity is a frequently under-documented HCC because providers often write 'obesity' without the morbid qualifier even when the BMI supports it. Query the provider when BMI documented is >= 40.

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.

Child Codes

E66.01Morbid (severe) obesity due to excess calories
HCC 48
E66.09Other obesity due to excess calories

Code Hierarchy

└E66Overweight and obesity└E66.0Obesity due to excess calories└E66.01Morbid (severe) obesity due to excess calories
└E66.01Morbid (severe) obesity due to excess calories

Also searched as

  • morbid obesity
  • severe obesity due to excess calories

Because E66.01 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

E66.01 maps to CMS-HCC V28 category 48, Morbid Obesity. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because E66.01 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

More on E66.01

Related condition guides

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