Health Calculators
Three free tools for understanding body metrics and energy needs: BMI (WHO ranges), BMR (Mifflin-St Jeor equation) and daily calorie needs. Each explains its formula, shows worked examples, and cites its sources — for education, not medical advice.
What can you calculate with these health tools?
Three connected numbers describe most day-to-day energy and weight questions: BMI (body mass index — weight in kg divided by height in metres squared) screens weight status against the WHO ranges; BMR (basal metabolic rate, estimated with the Mifflin-St Jeor equation) is the energy your body burns at complete rest; and daily calorie needs (TDEE) multiply BMR by an activity factor between 1.2 and 1.9. Each calculator explains its equation and shows worked examples.
How do BMI, BMR and calorie needs fit together?
BMI tells you where your weight stands today; BMR and TDEE tell you what it takes to change it. A sustained deficit of about 500 kcal per day below TDEE corresponds to roughly 0.45 kg (1 lb) of weight loss per week, which is within the 1–2 lb per week pace commonly recommended by health authorities. Use the BMI Calculator to set the goal and the Calorie Calculator to plan the path.
How accurate are these calculators?
They use the standard published equations (WHO BMI ranges; Mifflin-St Jeor, which validation studies found accurate to within 10% of measured resting energy expenditure for most adults), but they are screening estimates, not diagnoses. Athletes with high muscle mass, older adults, and pregnant women should interpret BMI cautiously and consult a healthcare provider for individual advice.
Frequently asked questions
The WHO defines a healthy BMI for adults as 18.5 to 24.9. Below 18.5 is classified underweight, 25 to 29.9 overweight, and 30 or above obese. BMI is a screening tool — it does not distinguish muscle from fat, so pair it with other measures where possible.
General guidance ranges from about 1,600 to 2,400 kcal per day for adult women and 2,000 to 3,000 kcal for adult men, depending on age and activity level. Your personal number is your BMR multiplied by an activity factor — the Calorie Calculator estimates it from your stats.
BMR is the energy your body uses at complete rest for breathing, circulation and cell repair; TDEE (total daily energy expenditure) adds everything else — movement, exercise and digestion. TDEE is typically 1.2 to 1.9 times BMR depending on how active you are.
No. They implement standard published formulas for education and self-screening, but they cannot account for your medical history. Consult a doctor or registered dietitian before making significant changes to diet or exercise.