Calorie calculator
A kilogram of body fat holds roughly 7,700 kcal, so losing half a kilogram a week means eating about 550 kcal a day less than you burn. That arithmetic is the whole basis of every calorie target, and it is an approximation — the body adapts as weight falls.
An estimate from a population equation. Individual metabolisms vary by roughly 10% either way, and the figure ignores illness, medication and pregnancy. Anyone eating below about 1,500 kcal a day should be doing it with medical supervision.
Daily calorie need is resting metabolic rate multiplied by an activity factor, then adjusted for your goal. The Mifflin–St Jeor equation estimates resting rate from weight, height, age and sex. Losing half a kilogram a week means a deficit of about 550 calories a day, since a kilogram of fat holds roughly 7,700 calories.
How to use this calculator
Activity level is where the estimate goes wrong most often. People pick "moderate" for three gym sessions a week while sitting down for the rest of it, which can overstate the target by three or four hundred calories a day — enough to cancel the deficit entirely. If the weight is not moving after a fortnight, the honest fix is usually to drop one activity band rather than to cut further.
Questions
Mifflin–St Jeor, published in 1990. It is the one most dietitians use, and it predicts resting rate more accurately than the older Harris–Benedict equation for modern populations.