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E66.9ICD-10-CM

Obesity, unspecified

BillableE66 is not billableA BMI code is required alongsideCarries no risk adjustment value

How the code is built

E

Chapter

Endocrine, nutritional and metabolic diseases

66

Category

Overweight and obesity

9

Char 4

Type and class not specified

Chapter

E00 to E89

Endocrine, nutritional and metabolic diseases

Block

E65 to E68

Overweight, obesity and other hyperalimentation

Category

E66

Overweight and obesity, not billable on its own

Billable

Yes

Complete at 4 characters

Use additional at E66

A body mass index code, if known

Adult or pediatric range

Editor flag

Not usually sufficient for admission

As a principal diagnosis

Risk adjustment

Does not map

While two of its siblings do

DefinitionCode structureClinical pictureDocumentationDecision guideTabular listComparisonClaim contextRisk adjustmentDenialsSources

Key takeaways

  • E66.9 codes obesity when neither the cause nor the class is documented
  • E66 itself is not billable, so a fourth character is always required
  • A body mass index code accompanies the obesity code whenever the value is known
  • Class codes added in October 2024 require the provider to document the class, since the BMI ranges are not part of the code descriptors
  • It is billable, but two of its siblings carry risk adjustment value, and E66.9 carries none
1Definition

What ICD-10 code E66.9 means

E66.9 is the ICD-10-CM code for obesity, unspecified. It applies when a provider documents obesity without identifying a cause and without stating a class or severity.

E66 is the category header and cannot go on a claim. It reads overweight and obesity, and it holds everything from overweight through morbid obesity. A fourth character is always required, and which one applies depends on wording the provider controls rather than on numbers the coder can see.

Code

E66.9

Descriptor

Obesity, unspecified

Chapter

Endocrine, nutritional and metabolic diseases

Block

Overweight, obesity and other hyperalimentation

Category

E66, overweight and obesity

Billable

Yes

Use additional at E66

A code identifying body mass index, if known

Editor flag

Not usually sufficient justification for admission as a principal diagnosis

The category changed substantially in the FY 2025 code set, effective October 2024, and the change is recent enough that a good deal of published guidance predates it.

2Code structure

Two routes to specificity, and a class that must be stated

E66.9 has no subdivisions. What sits around it is a category that now offers two separate pathways to a more specific code.

The category in full

Obesity, no cause or class stated

E66.9

Overweight

E66.3

Obesity due to excess calories, not morbid

E66.09

Morbid or severe obesity due to excess calories

E66.01

Drug-induced obesity

E66.1

Morbid obesity with alveolar hypoventilation

E66.2

Obesity, class 1

E66.811

Obesity, class 2

E66.812

Obesity, class 3

E66.813

Other obesity not elsewhere classified

E66.89

The two pathways are different in kind. The E66.0 route classifies by cause, meaning excess calories, and by whether the obesity is morbid. The E66.81 route classifies by class, which corresponds to established body mass index bands. A coder can arrive at a specific code either way, depending on how the provider wrote the note.

The class codes carry a constraint that catches people out. The body mass index ranges are not part of the code descriptors and are not inclusion terms. A class code can only be assigned when the provider documents the class, not derived from a body mass index value in the chart. A note recording a body mass index of 37 does not by itself support class 2 obesity.

And published advice on this has been reversed. Guidance issued before October 2024 directed that class 3 obesity be coded as morbid obesity due to excess calories. With the class codes now available, the specific class is coded when the provider states it. Whether a class 3 code and a morbid obesity code may both appear has remained contested, with the official position resting on what the documentation actually says.

3Clinical picture

Clinical findings documented under E66.9

Obesity is established by measurement, and the record usually contains more than the code reflects.

Anthropometric

Height, weight, body mass index, waist circumference

Class or severity

The provider's statement of class, or of morbid or severe obesity

Cause

Excess calorie intake, medication effect, or an endocrine contributor

Comorbidity

Type 2 diabetes, hypertension, obstructive sleep apnea, osteoarthritis, dyslipidemia

Functional impact

Mobility limitation, exertional dyspnea, effect on daily activities

Management

Counselling, nutrition referral, pharmacotherapy, surgical evaluation

Body mass index is the finding that most often exists in the chart and never reaches the claim. It does not change the obesity code, but it is separately reportable, and it is what most coverage criteria are built on.

4Documentation

What the chart must show

  • A provider-stated diagnosis of obesity, since the diagnosis itself cannot come from another clinician
  • Body mass index as a value, which may be recorded by a nurse, dietitian, or other clinician
  • The class, in the provider's words, if a class code is intended
  • Whether the obesity is morbid or severe, in the provider's words, if that code is intended
  • The cause, where identified, particularly a medication effect
  • Comorbid conditions, each coded separately
  • The management plan, including any referral for surgical or behavioral treatment

Authorship splits in an unusual way on this code. The body mass index code may be assigned from documentation by a clinician who is not the patient's provider, because it records a measurement. The obesity diagnosis itself must be documented by the provider. So a chart with a nurse-recorded body mass index of 42 and no provider diagnosis supports a body mass index code and no obesity code at all.

5Decision guide

When to assign E66.9, and when not to

Obesity, no cause or class

E66.9, plus the body mass index code

Overweight

E66.3

Obesity due to excess calories

E66.09

Morbid obesity, or severe obesity, due to excess calories

E66.01

Class 1 obesity

E66.811

Class 2 obesity

E66.812

Class 3 obesity

E66.813

Obesity caused by a medication

E66.1, with the drug identified

Morbid obesity with alveolar hypoventilation

E66.2

Another named form of obesity

E66.89

A body mass index value with no provider diagnosis

The body mass index code alone, then query

A body mass index in a class range, with no class stated

E66.9 or the cause-based code, since class must be documented

Obesity in pregnancy

The obstetric code, with the obesity code as directed

Query rather than default when a body mass index sits in the vitals, and the assessment says only obesity, and when the provider writes severe or class without the other detail the chosen code requires.

6Tabular list

Instructional notes at E66 and above

Use additional at E66

Code to identify body mass index, if known, using the adult or the pediatric range

Excludes1 at E66.01

Obesity with alveolar hypoventilation (E66.2)

Editor flag at E66.9

Not usually sufficient justification for admission to an acute care hospital as a principal diagnosis

The category is unusually light on prohibitions and unusually heavy on a single requirement.

The body mass index instruction is the operative note, and it sits at the category rather than at the code line. It applies to every E66 code, and the accompanying code differs for adults and children. Pediatric body mass index codes were themselves expanded alongside the class codes, adding percentile-based options that correspond to the three classes.

The morbid obesity and hypoventilation codes are mutually exclusive. Obesity with alveolar hypoventilation has its own code, and it cannot be paired with the morbid obesity code.

7Comparison

Codes frequently confused with E66.9

E66.3

Descriptor

Overweight

Use instead when

Overweight rather than obesity is documented

E66.01

Descriptor

Morbid (severe) obesity due to excess calories

Use instead when

The provider documents morbid or severe obesity from excess calories

E66.09

Descriptor

Other obesity due to excess calories

Use instead when

Excess calorie obesity is documented without morbid or severe

E66.1

Descriptor

Drug-induced obesity

Use instead when

A medication is documented as the cause

E66.2

Descriptor

Morbid (severe) obesity with alveolar hypoventilation

Use instead when

Hypoventilation accompanies the obesity

E66.811

Descriptor

Obesity, class 1

Use instead when

The provider documents class 1

E66.812

Descriptor

Obesity, class 2

Use instead when

The provider documents class 2

E66.813

Descriptor

Obesity, class 3

Use instead when

The provider documents class 3

E66.89

Descriptor

Other obesity not elsewhere classified

Use instead when

Another named form is documented

Z68.1 to Z68.45

Descriptor

Body mass index, adult ranges

Use instead when

Reported alongside the obesity code

Z68.5-

Descriptor

Body mass index, pediatric percentile ranges

Use instead when

Reported alongside for a child or adolescent

E65

Descriptor

Localized adiposity

Use instead when

Localized fat deposition rather than generalized obesity

E67.-

Descriptor

Other hyperalimentation

Use instead when

Another form of overnutrition is documented

R63.5

Descriptor

Abnormal weight gain

Use instead when

Weight gain is documented without an obesity diagnosis

G47.33

Descriptor

Obstructive sleep apnea

Use instead when

Sleep apnea is documented, reportable alongside

Z98.84

Descriptor

Bariatric surgery status

Use instead when

The patient has had bariatric surgery

The two class routes deserve one more note. E66.01 and E66.813 describe overlapping clinical territory, and each reaches it by different documentation. Which one the chart supports depends entirely on the words the provider used.

8Claim context

Services commonly reported with E66.9

E66.9 supports primary care and specialty evaluation and management, nutrition counselling, and the medical and surgical management of obesity.

The two Medicare benefits attached to obesity are both governed nationally, and both key on body mass index rather than on the diagnosis code. Intensive behavioral therapy for obesity is a covered preventive service delivered in a primary care setting, with a body mass index threshold and a defined visit schedule. Bariatric surgery is covered under a national determination with criteria that include a body mass index threshold, documented comorbidity, and prior unsuccessful medical management.

The practical consequence is the same for both. A claim carrying E66.9 does not establish either set of criteria. The body mass index code does part of the work, and the documented class or morbid status does the rest. A surgical authorization built on an unspecified obesity code will be returned.

Confirm the applicable national determination for surgical and behavioral services, and the contractor's policy for nutrition counselling and any pharmacotherapy administered in the office.

9Risk adjustment

What E66.9 does to a risk score

The specific codes split, and two of them pay nothing

E66.9 does not map to a risk adjustment category.

Neither do the class 1 and class 2 codes added in October 2024. Morbid obesity due to excess calories and class 3 obesity both do.

That produces a genuinely counterintuitive result.

Documenting class 2 obesity is more specific than documenting obesity, and it carries no more risk adjustment value than the unspecified code. Specificity and payment do not move together in this category the way they do in most others.

The undercoding pattern is the one auditors and consultants cite most.

A chart where the provider wrote morbid obesity and the claim went out with E66.9 is both a documentation-to-code mismatch and a lost capture. It runs in the opposite direction from most audit exposure, which is usually about overstating rather than understating.

Overstating carries its own risk.

Assigning morbid obesity from a body mass index value without a provider statement of morbid or severe obesity, or assigning a class code without a documented class, is an audit finding regardless of what the measurement shows.

Report it every year.

Risk adjustment does not carry a condition forward, and obesity is chronic, so the capture depends on the condition being documented and addressed at a face-to-face encounter each year.

10Denials

Coding errors that cause denials

Submitting E66 without a fourth character

Complete the code, since the category is not billable

Omitting the body mass index code

Add it, per the use additional instruction in the category

Coding E66.9 when the provider documented morbid or severe obesity

Assign E66.01

Deriving a class code from a body mass index value

Query, since the class must be documented and the ranges are not in the descriptors

Assigning morbid obesity from a measurement alone

Query for a provider statement

Assigning an obesity code from a nurse-recorded body mass index with no provider diagnosis

Report the body mass index code only, and query

Reporting E66.01 with the hypoventilation code

Choose one, since the Excludes1 prohibits the pair

Using an adult body mass index code for a pediatric patient

Use the pediatric percentile range

Building a bariatric surgery authorization on E66.9

Document the class or morbid status and the body mass index

Reporting E66.9 as a principal diagnosis for an admission

Review, since the editor flags it as not usually sufficient

11Sources

Where to verify E66.9

ICD-10-CM Official Guidelines for Coding and Reporting

The rule permitting body mass index assignment from non-provider clinician documentation, and the requirement that the associated diagnosis come from the provider

ICD-10-CM Tabular List at E66 and Z68

The use of additional instructions, the full category structure including the class codes, and the adult and pediatric body mass index ranges

CMS ICD-10 code page and the FY 2025 and FY 2026 files

The October 2024 addition of the obesity class codes and the pediatric body mass index expansion

CDC adult obesity ICD-10-CM code fact sheet

The class definitions and the intent behind the new codes

CMS Medicare Advantage rates and statistics

The current payment year model file, which maps morbid obesity and class 3 obesity but not the unspecified or lower class codes

Medicare Coverage Database

The national determinations for bariatric surgery and for intensive behavioral therapy for obesity, and your contractor's policy for nutrition counselling

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Last reviewed August 2026

This page is a free reference for billing and coding teams and is not coding, legal, or clinical advice. Code selection depends on the documentation in the record and on the policy of the payer being billed. Verify every code, instructional note, and sequencing rule against the current ICD-10-CM files and the Official Guidelines for Coding and Reporting for the applicable date of service. ICD-10-CM is maintained by the CDC's National Center for Health Statistics and published by CMS. CPT is a registered trademark of the American Medical Association. TruCare is not affiliated with CMS, NCHS, the AHA, or the AMA.

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