BMR Calculator

Your basal metabolic rate is the energy your body uses doing nothing at all: keeping your heart beating, your lungs working, your brain running and your body at temperature while you lie completely still. It is the floor beneath every other number in nutrition, and for most people it accounts for somewhere around 60 to 70 percent of everything they burn in a day. This calculator uses the Mifflin-St Jeor equation, which has been the standard since 1990 and is generally the more accurate of the two common formulas for people who are not athletes. It shows the older Harris-Benedict result beside it, because a great deal of published material still quotes that one and the two can differ by a hundred calories or more for the same person. Because New Zealand nutrition panels are printed in kilojoules, the result is given in both units. BMR is not the number you eat to. Multiply it by an activity factor and you get total daily energy expenditure, which is the figure that matters for maintaining, losing or gaining weight, and that is shown here too. Treat all of it as an estimate: these equations are population averages, and an individual can sit ten percent either side of the prediction depending on muscle mass, thyroid function and genetics.

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1,755 Cal
basal metabolic rate (Mifflin-St Jeor)
BMR in kilojoules7,343 kJ
Daily needs at this activity2,720 Cal
Daily needs in kilojoules11,382 kJ
Harris-Benedict BMR1,825 Cal

An estimate from population equations. Individual metabolic rate can sit around ten percent either side depending on muscle mass and other factors. Not medical advice.

How it works

The Mifflin-St Jeor equation is 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age in years, then plus 5 for men or minus 161 for women. The revised Harris-Benedict equation uses different coefficients and generally returns a slightly higher figure. Total daily energy expenditure is the BMR multiplied by an activity factor between 1.2 for sedentary and 1.9 for very active. Kilojoules are calories multiplied by 4.184, which is the unit New Zealand food labels are required to use.

Worked example

Take the defaults: a 35 year old man, 80 kg and 180 cm. Mifflin-St Jeor gives 10 x 80 = 800, plus 6.25 x 180 = 1,125, minus 5 x 35 = 175, plus 5, which totals 1,755 calories a day at complete rest. In kilojoules that is 1,755 x 4.184, about 7,343 kJ. At a moderate activity factor of 1.55, daily needs are 1,755 x 1.55, about 2,720 calories or 11,382 kJ. Harris-Benedict for the same person returns about 1,825 calories, roughly 70 higher, which is the size of disagreement to expect between the two.

Related calculators

Data sources: the Mifflin-St Jeor equation was published in the American Journal of Clinical Nutrition in 1990; the revised Harris-Benedict equation dates from 1984. One nutritional calorie is 4.184 kilojoules.

Frequently asked questions

What is the difference between BMR and TDEE?

BMR is the energy your body uses at complete rest, keeping basic functions running. Total daily energy expenditure, or TDEE, is BMR multiplied by an activity factor and includes everything else you do. TDEE is the figure to eat to; BMR is the floor beneath it.

Which equation is more accurate, Mifflin-St Jeor or Harris-Benedict?

Mifflin-St Jeor, published in 1990, is generally considered more accurate for the modern general population and is the default here. Harris-Benedict dates from 1919 and was revised in 1984, and tends to return a slightly higher figure. Both are population averages rather than measurements of you.

Should I eat at my BMR to lose weight?

No. BMR is what your body uses at complete rest, so eating only that amount while also moving around creates a much larger deficit than intended. Weight change is normally planned against total daily energy expenditure, and any substantial restriction is worth discussing with a doctor or dietitian.