What is the Body Mass Index (BMI)?
The Body Mass Index, abbreviated as BMI, is an international measure to determine whether someone has a healthy weight relative to their height. The formula is simple: divide your weight in kilograms by the square of your height in metres. The result is a number used by doctors, dietitians and health organisations worldwide as a first indicator of weight-related health risks.
The formula was developed in the 19th century by Belgian mathematician Adolphe Quetelet and has since been refined by the World Health Organization (WHO). Although BMI is not a perfect measure, it provides a quick, free and reliable screening that anyone can do at home.
Formula
BMI = weight (kg) ÷ [height (m) × height (m)] — Example: 75 kg ÷ (1.78 × 1.78) = 23.7 — healthy weight.
How do you interpret your BMI score?
The WHO uses eight categories to show where your weight sits on the health scale. Use the table below as a reference:
| Category | BMI value | Status | Health risk |
|---|---|---|---|
| Severe underweight | < 16.0 | Underweight | Very high |
| Moderate underweight | 16.0 – 16.9 | Underweight | High |
| Mild underweight | 17.0 – 18.4 | Underweight | Elevated |
| Healthy weight | 18.5 – 24.9 | Normal | Low |
| Overweight | 25.0 – 29.9 | Overweight | Elevated |
| Obesity class I | 30.0 – 34.9 | Obese I | High |
| Obesity class II | 35.0 – 39.9 | Obese II | Very high |
| Obesity class III | ≥ 40.0 | Obese III | Extreme |
What do you do with your BMI result?
What does this mean for you?
If your BMI falls in the normal range (18.5–24.9) there are no direct risks from a weight perspective. Keep up your healthy habits.
A BMI that is too low may indicate malnutrition, an eating disorder or an underlying medical condition. Always consult a doctor or dietitian.
Overweight or obesity increases the risk of type 2 diabetes, cardiovascular disease, sleep apnoea and joint problems.
If your BMI is in the normal range
Maintain your current lifestyle and check your BMI annually. Also calculate your TDEE to monitor your energy balance and use the Macro Calculator for the right nutritional ratios. TDEE · Macro Calculator
If your BMI is too high
Combine a calorie deficit with regular exercise. Aim for a gradual loss of 0.5–1 kg per week for sustainable results without slowing your metabolism.
Tip
A loss of just 5–10% of your body weight already delivers significant health benefits: lower blood pressure, better blood sugar and less joint load.
If your BMI is too low
Focus on calorie-dense, nutrient-rich foods: nuts, avocado, oily fish and protein-rich products. Use the BMR Calculator to find out how many extra calories you need. BMR Calculator
The limitations of BMI
BMI is useful, but not a complete picture. Key limitations:
- •Muscle vs. fat mass: A bodybuilder can have a BMI of 28 while being in excellent health. BMI does not distinguish between muscle and fat.
- •Fat distribution: Belly fat is more dangerous than fat on hips and thighs. A waist circumference above 88 cm (women) or 102 cm (men) is an additional risk factor.
- •Age: Muscle mass decreases with age, making BMI less representative for older adults.
- •Ethnicity: For people of Asian descent, risk thresholds start at BMI 23 (overweight) and 27.5 (obesity).
- •Pregnancy: BMI is not a suitable measure during or shortly after pregnancy.
Remember
Use BMI as one data point, not as a final verdict. Combine it with waist circumference, body fat percentage and how you feel. Consult a doctor or dietitian if in doubt.