BMI & Daily Calorie Calculator

Accurate as a population screening tool, unreliable for any individual person. BMI divides weight by height squared and knows nothing else — not muscle, not bone density, not build, not where the weight sits. A rugby player and a sedentary person of the same height and weight get the same number, and only one of them should be concerned. It was designed in the 19th century to describe populations, not to assess patients. As a second check, a waist measurement under half your height is a better indicator for most adults, and it takes a tape measure rather than a calculator.

The tool estimates it in two steps. First the Mifflin-St Jeor equation gives your basal metabolic rate — what your body uses at complete rest, which is typically 60 to 70 per cent of the total. Then that is multiplied by an activity factor from 1.2 for a desk job to 1.9 for a physical one. The result carries about a 10 per cent margin either way between individuals of identical measurements, because metabolism genuinely differs. Treat it as a starting point: track what you actually eat for three or four weeks, see what your weight does, and adjust the number rather than the diet.

It is the conventional starting point, chosen because it produces roughly half a kilo a week and is small enough to be sustainable. Two caveats matter. Your body adapts: as you lose weight the requirement falls, so the same intake stops producing the same loss after a couple of months and the number needs recalculating. And a deficit taken below about 1,200 kcal for women or 1,500 for men makes adequate nutrition genuinely difficult, which is where a calculator stops being useful and a dietitian starts.