Calorie Calculator

Mifflin-St Jeor, step by step

The basal metabolic rate is BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men, or − 161 for women. The starting example is a 30-year-old man, 178 cm and 75 kg: 10 × 75 = 750, 6.25 × 178 = 1,112.5, 5 × 30 = 150, so BMR = 750 + 1,112.5 − 150 + 5 = 1,717.5 kcal.

Multiplying by the Moderate activity factor of 1.55 gives 2,662.1, rounded to 2,662 kcal in the Maintain box, with 2,162 kcal for Lose weight and 3,162 kcal for Gain weight. A woman with the same age, height and weight has a BMR of 1,551.5 kcal and a maintenance figure of 2,405 kcal.

Activity multipliers

The spread between the lowest and highest setting is about 1,200 kcal a day for the same person, so the activity choice matters more than any other input. People tend to pick too high. Someone with a desk job who trains three times a week usually belongs in Light or at most Moderate, because the training hours are small next to the sitting hours.

What the lose and gain targets assume

Both targets are fixed offsets of 500 kcal from the maintenance figure, whatever your size. For a large, active person that is a modest change; for a small, sedentary person it can be too aggressive. A 60-year-old woman of 155 cm and 50 kg with Sedentary selected has a BMR of 1,008 kcal and maintenance of 1,209 kcal, so the Lose weight box shows 709 kcal, which is below the level most guidelines consider safe without supervision. In that case use a smaller deficit of 250–300 kcal, or add activity instead.

Imperial inputs

Feet and inches are combined and multiplied by 2.54, and pounds by 0.453592. The imperial starting example of 5 ft 10 in and 165 lb becomes 177.8 cm and 74.8 kg, giving a BMR of 1,714.7 kcal and 2,658 kcal at Moderate, slightly under the metric example because the person is a little shorter and lighter. The metric and imperial modes keep separate fields, so values are not converted when you switch.

How accurate the estimate is

• Mifflin-St Jeor predicts measured resting energy expenditure within about 10% for most adults, which at 2,600 kcal is a margin of roughly 260 kcal either way.
• It uses total weight, so a very muscular person is underestimated and a person with high body fat is overestimated.
• The equation was developed on adults; it is not designed for children, pregnancy or people with thyroid and other metabolic conditions.
• The figures are rounded to whole kilocalories, and an age of 0 or an empty field hides the result.
• Treat the output as a starting point: track your weight for two to three weeks and move the intake by 100–200 kcal if the trend is not what you intended.