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Calculate your Body Mass Index instantly. Understand what your number means and what a healthy range looks like for you.
BMI is calculated by dividing your weight in kilograms by the square of your height in metres: BMI = kg ÷ m². For imperial measurements, the formula is: BMI = (lbs ÷ in²) × 703. The result is a single number that places you in one of four standard categories used by healthcare organisations worldwide.
Evidence-based answers to the most common questions about Body Mass Index.
According to the World Health Organization, a BMI between 18.5 and 24.9 is considered a healthy weight range for most adults. A BMI below 18.5 indicates underweight, 25.0–29.9 indicates overweight, and 30.0 or above falls into the obese range. These thresholds apply to adults aged 20 and over; different charts are used for children and teenagers.
BMI is a useful screening tool but has significant limitations. It does not directly measure body fat — it estimates body size based on height and weight. As a result, it can misclassify people who are very muscular (labelling them overweight when they have little fat) and can also underestimate health risks in people who carry excess fat despite a "normal" weight. Healthcare professionals typically use BMI alongside other measurements — waist circumference, blood pressure, blood tests, and lifestyle factors — to get a complete picture of health.
The standard BMI formula and classification ranges are the same for both men and women. However, women naturally carry a higher percentage of body fat than men at the same BMI value due to physiological differences in muscle mass and fat distribution. Some researchers argue for gender-adjusted BMI thresholds, but the WHO standard categories remain the globally accepted reference point in clinical practice.
Research shows that people of Asian descent tend to have higher body fat percentages at lower BMI values compared to people of European descent. The WHO has published adjusted cut-off points for Asian populations, suggesting that health risks may begin at a BMI of 23.0 (rather than 25.0) for overweight, and 27.5 (rather than 30.0) for obesity. If you are of South Asian, East Asian, or Southeast Asian heritage, it's worth discussing these adjusted thresholds with your doctor.
The standard BMI categories apply to adults aged 20 and above regardless of age. However, body composition naturally changes with age — older adults tend to have more body fat and less muscle mass than younger adults at the same BMI. Some clinicians consider a BMI range of 23–29 acceptable for adults over 65, as being slightly heavier can protect against bone loss and the health risks of being underweight in older age. Always consult a healthcare provider for age-specific guidance.
BMI can be reduced by decreasing body weight through a combination of caloric deficit (eating less than you burn) and increased physical activity. However, a more meaningful goal than "lowering BMI" is improving overall body composition — reducing body fat while preserving or building muscle mass. A moderate caloric reduction of 500 calories per day, combined with 150–300 minutes of moderate exercise per week, is the approach recommended by most major health organisations for sustainable weight management.
BMI is a proxy measure derived from height and weight only. Body fat percentage (BFP) is a direct measurement of how much of your total body weight is fat tissue. BFP requires dedicated measurement tools such as DEXA scans, hydrostatic weighing, or bioelectrical impedance scales. While BMI is widely used due to its simplicity, body fat percentage is considered a more accurate indicator of metabolic health. A healthy body fat percentage is generally 6–24% for men and 16–30% for women, depending on age.
At a population level, BMI is strongly associated with increased risk of type 2 diabetes, cardiovascular disease, hypertension, and certain cancers at both ends of the spectrum (both very low and very high BMI). However, at an individual level, BMI is an imperfect predictor — many people with high BMIs live long, healthy lives, and some with normal BMIs develop metabolic disease. Waist circumference is often a better individual predictor of metabolic risk, as it more directly measures abdominal (visceral) fat, which is the type most strongly linked to disease.