BMR Calculator

Your basal metabolic rate is the energy you would burn lying still, awake, in a comfortable room, having fasted. It is the cost of simply staying alive: heart, lungs, brain, kidneys, liver and the constant repair of tissue. For most people it accounts for somewhere between 60 and 70 percent of all the calories they burn in a day, which is why it is the foundation of any calorie target.

The equation most dietitians now use is Mifflin-St Jeor, published in 1990 and found to be the most accurate of the widely available options for the general population, landing within about 10 percent of measured values for most people. It needs four inputs — weight, height, age and sex — and is linear in each of them. The revised Harris-Benedict equation from 1984 is the classic alternative; it is older and tends to read a few percent high for modern populations, but it is still in common use and is shown here for comparison.

Notice how each input pulls the number. Weight is the strongest factor, adding about 10 kcal per kilogram. Height adds roughly 6 kcal per centimetre. Each year of age subtracts about 5 kcal, reflecting the slow loss of lean tissue that accompanies ageing. Sex matters because men average more muscle: at identical height, weight and age, a man's BMR runs around 166 kcal higher than a woman's in the Mifflin formula.

BMR is not your daily calorie need. It ignores every movement you make, from walking to the kitchen to a hard training session. Multiply it by an activity factor to get your total daily energy expenditure, or use the TDEE calculator on this site. And remember these formulas are population averages: two people with identical stats can differ by 15 percent in measured metabolism, so treat the result as a starting point and adjust based on what the scale and your energy levels actually do over two to three weeks.

This calculator returns estimates for general information only. It is not medical advice, diagnosis or treatment, and it cannot replace an assessment by a qualified health professional. Individual results vary, and figures such as calorie needs, body-fat percentage and heart-rate zones are approximations based on population averages rather than measurements of you.