What is BMI?
BMI (Body Mass Index) is a measurement that uses your height and weight to estimate whether your body weight is healthy. It is calculated by dividing your weight in kilograms by the square of your height in metres.
Formula: BMI = weight (kg) ÷ height² (m²)
For example, a person who weighs 70kg and is 1.75m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9 — which is in the normal range.
BMI Categories
| BMI Range | Category | Health Risk |
|---|
| Below 18.5 | Underweight | Nutritional deficiency risk |
| 18.5 – 24.9 | Normal weight | Low risk |
| 25.0 – 29.9 | Overweight | Increased risk |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40.0 and above | Obese Class III | Extremely high risk |
Limitations of BMI
BMI is a useful screening tool but has important limitations:
- Athletes and bodybuilders may have a high BMI due to muscle mass, not fat
- Elderly people may have a normal BMI despite excess body fat due to muscle loss
- Different ethnicities may have different health risks at the same BMI
- BMI does not measure body fat distribution — where fat is stored matters too
Always consult a healthcare professional for a complete health assessment.
Frequently Asked Questions
What is a healthy BMI for adults? +
For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, the ideal range may vary slightly by age, sex and ethnicity. Asian populations, for example, may face health risks at lower BMI thresholds (23+).
Is BMI accurate for children? +
BMI for children and teenagers is calculated the same way but interpreted differently using age and sex-specific percentile charts. The adult BMI categories do not apply to children. Consult a paediatrician for child BMI interpretation.
What is BMI Prime? +
BMI Prime is your BMI divided by 25 (the upper limit of normal). A BMI Prime of 1.0 means you are exactly at the upper edge of normal. Below 1.0 is normal or underweight, above 1.0 is overweight or obese. It gives a quick sense of how far from normal you are.
How can I lower my BMI? +
To lower your BMI you need to reduce body fat through a combination of a calorie-controlled diet and regular exercise. A deficit of 500 calories per day typically leads to about 0.5kg weight loss per week. Use our Calorie Calculator to find your daily calorie target.
