What the Mifflin-St Jeor equation estimates your body uses in a day, at each level of activity.
This is a statistical estimate from a published equation, not a measurement and not nutritional advice. Individual metabolism varies with body composition, genetics, medication and health conditions that no formula sees.
The equation was derived in adults. Children, adolescents and pregnancy use different references entirely.
Estimated daily energy use
Basal rate multiplied by the activity factor — roughly what maintains current weight.
The equation lands within 10% for about four adults in five. Treat the range, not the single number, as the answer.
What the body uses at complete rest over 24 hours.
Everything is worked out in your browser. Nothing is sent anywhere.
The equation is Mifflin-St Jeor, published in 1990 and validated against indirect calorimetry — the method that measures energy use by analysing exhaled air. It is the equation the Academy of Nutrition and Dietetics recommends for adults, and it is more accurate than the Harris-Benedict formula most calculators still use, which overestimates by around 5% in the modern population.
More accurate is not accurate. It lands within 10% for roughly four adults in five, which means one in five is outside that band — and the equation cannot see body composition, thyroid function, medication or the metabolic differences that make two people of the same height, weight and age burn measurably different amounts. Two people can both be right about their inputs and see the same figure while actually differing by 400 kcal.
The activity multiplier is the largest source of error you control. One step up the scale adds about 15% — more than the equation’s own margin — and almost everyone overestimates: someone who trains twice a week is "light", not "active". The full scale is shown above precisely so the difference between the steps is visible rather than hidden behind one selected value.
Basal metabolic rate is what the body uses at complete rest over 24 hours — breathing, circulation, brain, cell repair. Daily energy use is that figure multiplied by an activity factor, which covers everything else, including digestion and simply moving around a room.
Within 10% for about 80% of adults. The range shown next to the number is the honest answer; the single figure is the midpoint of it. Only indirect calorimetry measures your actual rate, and no equation substitutes for it.
Because that would be advice about your body, and this page knows four numbers about you. What to eat depends on health conditions, medication, body composition, goals and history — a dietitian works with all of that, and an equation does not.
No. Mifflin-St Jeor was derived in adults, and both cases use entirely different references. The calculator refuses ages under 18 rather than returning a number that does not apply.
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