What is BMI?
Body Mass Index is a simple measure used by the World Health Organization to estimate whether an adult’s weight suits their height: BMI = weight (kg) ÷ height² (m). Someone weighing 70 kg at 1.70 m has a BMI of 70 ÷ 2.89 = 24.2.
Adult BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obesity class 1 |
| 35 – 39.9 | Obesity class 2 |
| 40+ | Severe obesity |
How to use it
- Choose metric (cm/kg) or imperial (ft/lb).
- Enter height, weight, age and sex.
- Pick your activity level honestly for a better calorie estimate.
- See your BMI on the color scale, your healthy weight range and your daily calories.
How daily calories are calculated
We use the Mifflin-St Jeor equation, one of the most accurate for estimating basal metabolic rate (BMR) — calories burned at complete rest — then multiply by an activity factor to get maintenance calories. A deficit of about 500 kcal/day typically leads to roughly 0.5 kg loss per week; the calculator never suggests going below a safe minimum.
Limitations
BMI does not distinguish fat from muscle, so muscular athletes may appear “overweight”. It is not suitable for children and teens (who use age-based percentile charts) or pregnant women. Use it as a general indicator and consult a doctor or dietitian before major changes.