What BMI is
NIDDK, the diabetes and kidney institute within the US National Institutes of Health, treats BMI as an estimate of overweight and obesity built from just two numbers, height and weight [1]. The BMI calculator on this site does the arithmetic if you need it.
Because it uses only two measurements, BMI does not show where weight is carried. The National Heart, Lung, and Blood Institute (NHLBI) adds waist size as a separate risk marker: more than 35 inches (about 89 cm) for women or 40 inches (about 102 cm) for men raises the risk of heart disease and type 2 diabetes [5]. NHLBI also advises talking to your clinician about what your BMI means for you.
The adult ranges
NIDDK and CDC use the same cut-offs for adults aged 20 and older. CDC splits obesity further into three classes and notes that the adult categories do not depend on age, sex or race [1][3].
| BMI | NIDDK category | CDC category |
|---|---|---|
| Under 18.5 | — | Underweight |
| 18.5–24.9 | Healthy weight | Healthy weight |
| 25–29.9 | Overweight | Overweight |
| 30–34.9 | Obesity | Class 1 obesity |
| 35–39.9 | Obesity | Class 2 obesity |
| 40 or more | Severe obesity | Class 3 obesity |
Where the 30 and 27 come from
NIDDK says clinicians use BMI to help judge who might benefit from a weight management medicine: an adult with a BMI of 30 or more, or 27 or more together with a weight-related problem, for example type 2 diabetes or hypertension. It adds that these medicines are not for everyone with a high BMI [2].
The same thresholds run through the trials. Wegovy®, Zepbound®, Saxenda® and Foundayo™ each enrolled adults with a BMI of 30 or more, or 27 to just under 30 plus a related condition, for example hypertension, dyslipidemia (abnormal blood fats) or sleep apnea. Their trials in type 2 diabetes used a BMI of 27 or more [6][7][8][9]. FDA’s November 2023 announcement of Zepbound® described its population in these same BMI terms [11].
What section 1 says today
Look for a BMI number in section 1 of the current US labels, Indications and Usage, and you will not find one for adults. Wegovy®, Zepbound®, Foundayo™ and Saxenda® simply name obesity, or overweight together with a weight-related condition [6][7][8][9].
The Saxenda® label shows that this wording changed: its list of recent major changes dates an update to the indication to May 2025 and records a patient selection subsection in the dosing section as removed at the same time [8]. The labels do not explain the reason. In practice, the diagnosis of obesity or overweight, and the decision to treat, rests with your prescriber.
Europe and Canada still write the numbers
Outside the US, the thresholds remain in the indication itself. The table compares the documents checked on 20 October 2026.
| Document | Adults | Other BMI conditions |
|---|---|---|
| US labels: Wegovy®, Zepbound®, Saxenda®, Foundayo™ [6][7][8][9] | Obesity, or overweight with a weight-related condition; no number | Zepbound® sleep apnea indication: adults with obesity |
| EU Wegovy® (injection and tablets) [12] | Initial BMI of 30 or more, or 27 to under 30 with a weight-related condition | 7.2 mg only for adults with a starting BMI of 30 or more |
| EU Mounjaro® [13] | Initial BMI of 30 or more, or 27 to under 30 with a weight-related condition | Diabetes indication has no BMI condition |
| Canada Wegovy® [14] | Initial BMI of 30 or more, or 27 or more with a weight-related condition | Heart indication: BMI of 27 or more |
| Canada Zepbound® [15] | Initial BMI of 30 or more, or 27 to under 30 with a weight-related condition | Sleep apnea: BMI of 30 or more |
BMI for teenagers
Children are not measured against the adult cut-offs. NHLBI says a child’s BMI should be compared with growth charts for their age and sex [5]. CDC defines obesity in children and teens as a BMI at or above the 95th percentile for sex and age, and severe obesity as 120% of that 95th-percentile value or more [4].
The Wegovy® pediatric trial enrolled 201 young people aged 12 and older whose BMI was at or above the 95th percentile for age and sex [6]. The Canadian Wegovy® monograph adds two more conditions for this age group: a body weight above 60 kg and an inadequate response to diet and activity alone [14]. The European information asks prescribers to stop and re-evaluate if a teenager’s BMI has not fallen by at least 5% after 12 weeks on the maintenance or highest tolerated dose [12].
Saxenda® uses two criteria for ages 12 and over: a body weight above 60 kg and a BMI matching an adult value of 30 or more by international cut-offs. Its label also uses BMI as a checkpoint for teenagers: after 12 weeks on the maintenance dose, prescribers are told to stop if BMI has not fallen by at least 1% [8].
Other places BMI appears
- Heart trials: the Wegovy® cardiovascular trial enrolled adults with established heart disease and a BMI of 27 or more; the Mounjaro® SURPASS-CVOT trial, in type 2 diabetes, required a BMI of 25 or more [6][10].
- Fatty liver: the Wegovy® MASH trial included some people with a BMI under 25, and the label notes limited information for that group. Its baseline table defines lean MASH using a lower cut-off for Asian participants (under 23) than for others (under 25) [6].
- Sleep apnea: the Zepbound® sleep apnea trials enrolled adults with obesity, defined as a BMI of 30 or more [7].
- Results: the Zepbound® and Foundayo™ labels report that weight reduction was seen regardless of baseline BMI, and Wegovy® says its cardiovascular benefit was not affected by BMI [6][7][9].
- Adults on Saxenda®: the US label uses weight rather than BMI as its checkpoint, asking prescribers to stop if at least 4% of body weight has not been lost after 16 weeks [8].
What BMI cannot tell you
BMI is a starting point, not a verdict. It does not show how much of your weight is fat or muscle, or how your blood pressure and blood sugar look, which is why NIDDK leaves the assessment of individual risk to your clinician [2]. CDC makes the same point when it calls BMI a screening measure to be weighed with other factors [3].
During treatment, BMI simply moves with weight, so the trend in weight and waist usually says more than a category name.
Wegovy® and Saxenda® are registered trademarks of Novo Nordisk A/S. Zepbound® and Mounjaro® are registered trademarks of Eli Lilly and Company; Foundayo™ is a trademark of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Novo Nordisk or Eli Lilly and Company.
