BMI calculator

BMI is your weight in kilograms divided by the square of your height in metres. A 70 kg adult at 175 cm has a BMI of 22.9. The adult bands are: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, and 30 or above obesity.

The healthy weight range shown above is simply those cut-offs worked backwards for your height — the weights that correspond to a BMI between 18.5 and 24.9.

BMI cannot distinguish muscle from fat. A well-trained athlete is routinely classed as overweight while carrying very little body fat, and someone with low muscle mass can sit in the healthy band while carrying more fat than is ideal. It also says nothing about where fat is stored, and fat around the abdomen carries more health risk than the same amount elsewhere.

It was designed to describe populations, not people. Average build differs between ethnic groups — the thresholds at which health risk rises are lower for people of South and East Asian descent, for instance — and the standard adult bands do not apply to children, pregnancy, or older adults, where a slightly higher BMI is often protective.

Treat a BMI outside the healthy range as a prompt for a conversation with a doctor, not a conclusion. Waist measurement, blood markers, fitness, and how your weight has changed over time all say more about health than this one ratio does.

If you want to change your weight, the practical question is not what your BMI is but what you burn and what you eat. The TDEE calculator estimates your maintenance calories, and the calorie deficit calculator turns a target weight and a pace into a daily number and a realistic timeline.

Body weight also moves for reasons that have nothing to do with fat — water, salt, glycogen, and digestion swing the scale by a kilogram or more from morning to morning. Weekly averages tell you far more than any single reading.