How it works
First your basal metabolic rate (calories burned at rest) is estimated, then multiplied by an activity factor to give your total daily energy expenditure — the calories that keep your weight steady.
About 7,700 kcal equals 1 kg of body fat, so eating 500 kcal a day less than maintenance loses roughly 0.5 kg a week. Losing more than 1 kg a week is hard to sustain and is best done with a doctor’s advice.
Women should not normally eat less than about 1,200 kcal a day and men less than about 1,500 kcal without medical supervision.