Health & Fitness Calculators

Understanding your BMI, BMR and calories

Body Mass Index divides weight in kilograms by height in metres squared. The WHO categories are: under 18.5 (underweight), 18.5–24.9 (healthy), 25–29.9 (overweight) and 30+ (obese). Your BMR (basal metabolic rate) is the energy your body uses at complete rest; multiply it by an activity factor and you get your TDEE — the calories you burn in a typical day. A deficit of about 500 calories a day corresponds to roughly half a kilo of fat loss per week.

Ideal weight and hydration

The ideal-weight tool uses the Devine formula, a clinical rule of thumb based on height and sex, alongside the healthy-BMI weight range for context. The water-intake estimate starts from roughly 33 ml per kilogram of body weight and adds extra for exercise. Both are general guides, not prescriptions.

These tools are for general information only and are not a substitute for professional medical advice.