2027 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
- Risk Adjusts — HCC 48
- 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 2027 (October 1, 2026 through September 30, 2027) 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.
For Medicare Advantage risk adjustment, E66.01 maps to CMS-HCC Category 48 (Morbid Obesity) under the V28 model, adding a risk factor of about 0.186 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
E66.01 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Morbid obesity
- Severe obesity
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to E66.01: its own notes plus those printed at E66 and Chapter 4. A note printed at a category, block or chapter applies to every code under it.
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- morbid (severe) obesity with alveolar hypoventilation (E66.2)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Code First
The underlying condition named in the note is sequenced before this code.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
Notes
General instructions on how these codes are used.
- All neoplasms, whether functionally active or not, are classified in Chapter 2. Appropriate codes in this chapter (i.e. E05.8, E07.0, E16-E31, E34.-) may be used as additional codes to indicate either functional activity by neoplasms and ectopic endocrine tissue or hyperfunction and hypofunction of endocrine glands associated with neoplasms and other conditions classified elsewhere.
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name E66.01, its category, or a range that includes it.
Excludes1 1
These codes carry an Excludes1 note naming E66.01: they are not reported together with it, unless the two conditions are unrelated.
Code First 1
These codes say to code first a condition named in the note, and E66.01 is one of the conditions named.
Use Additional Code 2
These codes say to use an additional code from the note, and E66.01 is one of the codes named.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
morbid E66.01
due to excess calories E66.01
severe E66.01
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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
What is the ICD-10 code for morbid (severe) obesity due to excess calories?
The ICD-10-CM code for morbid (severe) obesity due to excess calories is E66.01 (sometimes written as E6601). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
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, 2026 through September 30, 2027.
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 641, 640, with relative weights from 0.7864 to 1.3392 depending on complications. Higher weights mean higher Medicare reimbursement.
Can E66.01 be reported with E66.2?
Not as a rule. The Excludes1 note on E66.01 lists "morbid (severe) obesity with alveolar hypoventilation (E66.2)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
Does E66.01 need an additional code?
When the condition applies, yes. The Use Additional Code note at E66, which applies to E66.01, reads: code to identify body mass index (BMI), if known, for adults (Z68.1-Z68.45) or pediatrics (Z68.5-). The additional code is reported after E66.01.
What HCC is E66.01?
E66.01 (morbid (severe) obesity due to excess calories) maps to CMS-HCC Category 48 (Morbid Obesity), commonly written as HCC 48, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 22 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does E66.01 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, E66.01 adds a risk adjustment factor of about 0.186 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.118 to 0.442 depending on the payment segment). HCC 48 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 48 category page.
