BMR Calculator

Basal metabolic rate is the energy your body uses in a day at complete rest, for breathing, circulation, keeping warm and running the organs, before any movement or digestion. For most people it is the largest part of the day’s energy use: with the activity factors this site uses, from about half of it for the very active to more than four-fifths for the sedentary.

For most healthy adults, Mifflin–St Jeor. A 2005 systematic review for the American Dietetic Association found it predicted measured resting metabolic rate within 10% for more people than the other equations it tested. Harris–Benedict, first published in 1919 and revised in 1984, tends to read a little higher. Katch–McArdle can suit lean, muscular people better, provided the body-fat figure is reliable.

They were fitted to different groups of people in different decades. Harris and Benedict measured volunteers in 1919, revised with more data in 1984; Mifflin and St Jeor measured 498 adults in 1990; Katch–McArdle uses lean mass alone and ignores age and sex. A spread of about 100 kcal between them is normal, and a reminder that each figure is an estimate, not a measurement.

Nearly. BMR is measured under strict conditions: after a night’s sleep, 12 hours without food, lying still in a warm room. RMR is measured under looser ones and usually reads slightly higher, often by up to 10%. The equations here are used for both, and the gap is smaller than their own error.

Multiply it by an activity factor, from 1.2 for a desk job with no exercise to 1.9 for a physical job or twice-daily training. The product is your total daily energy expenditure: the TDEE Calculator shows it at all five levels, and the Calorie Calculator turns it into targets for losing, holding or gaining weight.