Calorie calculator

How the estimate is made

The calculator uses the Mifflin-St Jeor equation from 1990, which studies have found the most accurate of the common formulas for adults. It estimates the energy your body uses at rest (the basal metabolic rate, BMR):

• Men: 10 × weight in kg + 6.25 × height in cm − 5 × age + 5
• Women: 10 × weight in kg + 6.25 × height in cm − 5 × age − 161

That figure is then multiplied by an activity factor to give your total daily energy expenditure (TDEE), the calories that keep your weight steady:

The calculator opens on a 30-year-old woman, 165 cm and 65 kg, lightly active: a BMR of 1,370 and 1,884 calories a day to stay at that weight. A 40-year-old man of 180 cm and 80 kg who exercises 3 to 5 days a week has a BMR of 1,730 and needs about 2,682.

Losing or gaining weight, a week at a time

The goals use the common rule that a kilogram of body fat holds about 7,700 calories (a pound about 3,500). Losing 0.5 kg a week therefore means eating about 550 calories a day below maintenance; losing a pound a week means about 500 fewer. For the example woman, 0.5 kg a week is 1,334 calories a day.

Faster goals push the number low. When a goal falls under 1,200 calories a day for a woman or 1,500 for a man, the line is marked Very low: ask a doctor first, because diets that low make it hard to get enough nutrients and are usually only followed with medical support. Health services such as the NHS and the CDC suggest losing no more than 0.5 to 1 kg (1 to 2 pounds) a week.

Why your real number may differ

Any equation is an average for people of your size and age. Muscle burns more than fat, so very muscular people burn more than it predicts; some people burn a few hundred calories more or less for reasons no formula captures. Food labels and fitness trackers have their own errors too.

The practical way to use the estimate is to eat close to it for two or three weeks while weighing yourself under the same conditions, then adjust by 100 to 200 calories a day if your weight moves differently from what you wanted. Weight lost slows the burn a little, so recalculate after every few kilograms. The calculator is not meant for anyone pregnant or breastfeeding, under 18 or managing a health condition: ask a doctor or a dietitian. The BMI calculator beside it shows where a weight sits for your height.