2026 ICD-10-CM Diagnosis Code E66.01Morbid (severe) obesity due to excess calories
ICD-10-CM Codes›E00–E89›E65-E68›E66
- Billable — Valid for Submission
- Chronic Condition
E66.01 is a billable ICD-10-CM diagnosis code for morbid (severe) obesity due to excess calories. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 640 through 641. Coders also document this condition as morbid obesity. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Obesity.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Morbid obesity
- Obese class III
- Severe obesity
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Type 1 Excludes
- morbid severe obesity with alveolar hypoventilation E66.2
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
- due to
- morbid - E66.01
- due to excess calories - E66.01
- severe - E66.01
External Cause of Injuries IndexGuidance
References for this code in the External Cause of Injuries Index.
- Obesity
- due to
- excess calories
- morbid
- Obesity
- due to
- excess calories
- severe
- Obesity
- morbid
- Obesity
- morbid
- due to excess calories
- Obesity
- severe
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Morbid Obesity
an excess of body weight, normally defined as an individual with a body mass index greater than 35 or a body weight greater than one hundred percent of ideal body weight.
Patient EducationClinical
Obesity
Obesity is a disease that means having too much body fat. It is different from being overweight, which means weighing too much. Both terms mean that your weight is greater than what's considered healthy for your height.
The full article covers:
- What is obesity?
- What raises your risk of obesity?
- How is obesity diagnosed?
- What health problems can obesity cause?
- What are the treatments for obesity?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert E66.01 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About E66.01Overview
Is E66.01 (Obesity due to excess calories) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report morbid (severe) obesity due to excess calories on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does E66.01 group to?
When morbid (severe) obesity due to excess calories is the principal diagnosis on an inpatient stay, it groups to MS-DRG 640, 641, with relative weights from 0.7782 to 1.3356 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of E66.01?
Under the General Equivalence Mappings, morbid (severe) obesity due to excess calories converts to ICD-9-CM 278.01 (morbid obesity). The mapping is approximate, so confirm the match fits the documentation.
Footnotes
[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:
- The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
- The condition places limitations on self-care, independent living, and social interactions.
