BMI
Also known as: Body Mass Index, Quetelet Index
BMI stands for Body Mass Index, a measure calculated by dividing weight in kilograms by height in meters squared (kg/m²). BMI is used to classify weight status and is a common eligibility criterion for obesity medications like semaglutide and tirzepatide. While useful for populations, BMI has limitations for individuals.
Last updated: January 21, 2026
BMI Calculation
Formula
BMI = Weight (kg) / Height (m)²Example
- Weight: 90 kg (198 lbs)
- Height: 1.75 m (5’9”)
- BMI = 90 / (1.75)² = 90 / 3.06 = 29.4
Imperial Conversion
BMI = [Weight (lbs) / Height (in)²] × 703BMI Categories
| BMI | Classification | Health Risk |
|---|---|---|
| <18.5 | Underweight | Increased |
| 18.5-24.9 | Normal | Baseline |
| 25-29.9 | Overweight | Increased |
| 30-34.9 | Class I Obesity | High |
| 35-39.9 | Class II Obesity | Very High |
| ≥40 | Class III Obesity | Extremely High |
BMI for Medication Eligibility
GLP-1 Agonists (Obesity Indication)
| Medication | Typical Eligibility |
|---|---|
| Wegovy/Zepbound | BMI ≥30, or ≥27 with comorbidity |
| Saxenda | BMI ≥30, or ≥27 with comorbidity |
Comorbidities That Lower Threshold
- Type 2 diabetes
- Hypertension
- Dyslipidemia
- Sleep apnea
Limitations of BMI
What BMI Doesn’t Measure
| Factor | BMI Blind Spot |
|---|---|
| Body composition | Doesn’t distinguish fat vs muscle |
| Fat distribution | Doesn’t identify visceral fat |
| Fitness level | Athletes may be “obese” by BMI |
| Metabolic health | Can’t identify metabolically healthy obesity |
| Age effects | Muscle loss with age not captured |
Examples of BMI Failure
- Muscular athlete: BMI 32, but 10% body fat
- Sedentary person: BMI 24, but 35% body fat
- Same BMI, very different health status
BMI and Ethnicity
Different populations have different risk thresholds:
| Population | Obesity Threshold |
|---|---|
| Standard (European) | BMI ≥30 |
| Asian populations | BMI ≥27.5 |
| Some guidelines | BMI ≥25 for Asians |
Asian populations tend to have higher body fat percentage at lower BMIs and higher cardiometabolic risk.
Better Alternatives?
| Measure | What It Captures |
|---|---|
| Waist circumference | Visceral fat (over 40” men, over 35” women = risk) |
| Waist-to-hip ratio | Fat distribution |
| Body fat percentage | Actual adiposity |
| Waist-to-height ratio | Simple risk indicator |
| DEXA scan | Detailed body composition |
Why BMI Persists
- Simple and cheap
- No equipment needed
- Established reference ranges
- Population-level validity
- Insurance and guidelines use it
BMI in Clinical Practice
Useful For
- Screening tool
- Population studies
- Tracking trends
- Treatment eligibility
Should Be Combined With
- Clinical assessment
- Waist measurement
- Comorbidity evaluation
- Patient history
BMI Changes with Weight Loss
What to Expect
| Weight Loss | BMI Change (5’9” person) |
|---|---|
| 10 lbs (4.5 kg) | ~1.5 BMI points |
| 20 lbs (9 kg) | ~3 BMI points |
| 50 lbs (23 kg) | ~7.5 BMI points |
GLP-1 Agonist Outcomes
Typical BMI reduction: 4-7 points Example: BMI 35 → BMI 28-31
Frequently Asked Questions
Is BMI accurate for me as an individual?
BMI is a screening tool, not a diagnostic. It works well for populations but may misclassify individuals, especially those who are muscular, very short/tall, or from certain ethnic backgrounds. Consider it one data point among many.
What if my BMI is “normal” but I feel unhealthy?
BMI doesn’t capture metabolic health, fitness, or body composition. You can have a normal BMI but high body fat percentage, poor metabolic markers, or low fitness. A comprehensive health assessment includes more than BMI.
Should I aim for a specific BMI?
Rather than targeting a BMI number, focus on health improvements: better metabolic markers, increased fitness, sustainable habits. The optimal BMI varies by individual. Discuss realistic goals with your healthcare provider.
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Disclaimer: This glossary entry is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider for medical questions.