Adult BMI guide
Adult BMI Categories (CDC): Underweight, Healthy, Overweight & Obesity — 2026
BMI categories group adult BMI results into broad screening ranges. They are helpful for understanding where a result sits compared with standard adult cutoffs, but they are not a diagnosis and they do not describe a person's full health picture.
Quick answer
The CDC defines four adult BMI categories: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), and obesity (30.0 and above). Obesity is further split into Class I (30–34.9), Class II (35–39.9), and Class III (40+). These bands apply to adults aged 20 and older.
Complete adult BMI category table
The table below uses common adult BMI cutoffs. It includes obesity classes because many public health references use those classes when BMI is 30 or above.
| BMI range | Category | What it usually means |
|---|---|---|
| Below 18.5 | Underweight | Weight may be below the standard adult reference range for height. |
| 18.5 to 24.9 | Healthy weight | Weight is within the commonly used adult healthy BMI range. |
| 25 to 29.9 | Overweight | Weight is above the standard healthy BMI range for height. |
| 30 to 34.9 | Obesity class I | BMI falls in the first obesity class used for adult screening. |
| 35 to 39.9 | Obesity class II | BMI falls in the second obesity class used for adult screening. |
| 40 or above | Obesity class III | BMI falls in the highest standard adult obesity class. |
What each category means
Underweight: BMI is below the adult reference range. Low BMI can have many causes, including nutrition, illness, medication, or body type.
Healthy weight: BMI is within the common adult reference range. This does not guarantee metabolic health or measure fitness.
Overweight: BMI is above the healthy range. Waist circumference, activity, and health history can add important context.
Obesity classes: BMI is 30 or above. Classes I, II, and III describe progressively higher BMI ranges, but still require clinical context.
Practical examples
| Example | BMI | Category |
|---|---|---|
| 1.70 m and 60 kg | 20.8 | Healthy weight |
| 1.70 m and 78 kg | 27.0 | Overweight |
| 1.70 m and 92 kg | 31.8 | Obesity class I |
| 5 ft 9 in and 150 lb | 22.1 | Healthy weight |
| 5 ft 9 in and 210 lb | 31.0 | Obesity class I |
Obesity classes explained
The CDC splits obesity into three classes because health risk rises across the band. All three still begin at BMI 30, the point where the broad obesity category starts.
| Class | BMI range | Common label |
|---|---|---|
| Class I | 30.0 to 34.9 | Moderate obesity |
| Class II | 35.0 to 39.9 | Severe obesity |
| Class III | 40.0 or above | Very severe obesity |
Class III (BMI 40+) is sometimes described as severe or extreme obesity in clinical settings and is where specialist interventions are most often considered. As always, the class is a screening band, not a diagnosis.
Why the CDC and NHS use the same thresholds
The adult bands — below 18.5, 18.5 to 24.9, 25 to 29.9, and 30 or above — come from the World Health Organization and are adopted by both the CDC in the US and the NHS in the UK. That is why a search for CDC adult BMI categories returns the same numbers you would find on an NHS page. For adults, the classification is international and consistent, so you can use the same table wherever you are.
Limits of BMI categories
BMI is useful because it is simple, but the category can be less accurate for athletes and people with high muscle mass, older adults with lower muscle mass, pregnancy, some ethnic groups, and people with medical conditions that affect fluid balance or weight. Adult BMI categories should not be used to classify children or teenagers.
If your category is unexpected, combine BMI with waist circumference, recent weight changes, medical history, and professional guidance. A qualified clinician can interpret your result alongside information an online calculator cannot collect.
BMI category FAQ
What are the CDC adult BMI categories?
Underweight (below 18.5), healthy weight (18.5 to 24.9), overweight (25.0 to 29.9), and obesity (30.0 and above), with obesity split into Class I, II and III.
What BMI is underweight for adults?
Below 18.5. The CDC classes any adult BMI under 18.5 as underweight.
What is the normal or healthy adult BMI range?
18.5 to 24.9. This is the healthy-weight band for adults aged 20 and older.
At what BMI does obesity start?
At 30.0. A BMI of 30 or above is obesity; 30 to 34.9 is Class I, 35 to 39.9 is Class II, and 40+ is Class III.
What is the overweight BMI range?
25.0 to 29.9, between the healthy band and obesity.
Are the CDC and NHS BMI categories the same?
Yes, for adults. Both use the World Health Organization thresholds: below 18.5, 18.5 to 24.9, 25 to 29.9, and 30+.
Are BMI categories a diagnosis?
No. BMI categories are screening ranges. They can guide a conversation, but they do not diagnose health, body fat, or disease risk for an individual.
Why do some sources say obesity starts at 30?
The broad obesity category begins at BMI 30. Some clinical and public health references subdivide that range into class I, II, and III to describe severity more clearly.
Do BMI categories apply to children?
No. Children and teenagers need age- and sex-specific BMI percentiles rather than fixed adult ranges.
Can a healthy BMI still miss health risks?
Yes. BMI does not show waist circumference, blood pressure, blood sugar, cholesterol, fitness, or family history.
Can a high BMI be misleading?
Yes. Athletes and people with high muscle mass may have a higher BMI without the same body fat level as another person with the same score.
When should I ask for professional advice?
Consider speaking with a qualified healthcare professional if your BMI result concerns you, your weight changed unexpectedly, or you have symptoms, pregnancy, a medical condition, or a history of disordered eating.
References
Medical disclaimer
This page is for general informational use only and is not a substitute for professional medical advice, diagnosis, or treatment.