BMR calculator
For a typical desk worker, basal metabolic rate accounts for around 60 to 70 per cent of total daily energy use. Digestion takes another ten. Deliberate exercise — even a solid hour of it — is usually the smallest slice. That is why diet changes move weight faster than exercise does, and why "burning off" a large meal takes considerably longer than eating it did.
An estimate from a population equation. Individual metabolic rate varies by 10–15% from the predicted figure even between people of identical size, and more if body composition is unusual.
Basal metabolic rate is the energy your body uses at complete rest. The Mifflin–St Jeor equation puts a 30-year-old man of 175 cm and 75 kg at about 1,699 kcal a day; multiply by an activity factor of 1.2 to 1.9 for total daily expenditure.
How to calculate BMR
Mifflin–St Jeor replaced the older Harris–Benedict equation in 1990 because it predicts measured resting rate more accurately across modern body compositions, and it remains the standard recommendation. Both are population equations, so an individual can sit 10 to 15 per cent either side of the prediction for reasons the formula cannot see — thyroid function, lean mass, and how much non-exercise movement a person does without noticing. The honest way to use any of these numbers is as a starting point that you then correct against two weeks of actual weight change.
Questions
The energy your body uses at complete rest to run its basic functions — breathing, circulation, cell repair.