BMR calculator, your resting energy.

A BMR calculator estimates your basal metabolic rate: the energy your body uses in a day just to stay alive at rest, with no movement and no meals to digest. This one uses two published equations, Mifflin-St Jeor and Harris-Benedict, shows both results next to each other and writes out the sums. BMR is not the number of calories you eat to stay the same weight, because it leaves out all movement. For that, see the TDEE calculator.

How to use the BMR calculator

1. Pick Units: metric, US or UK. Switching converts the height and weight you typed.
2. Type your Age and choose your Sex. Both equations were fitted separately for men and women, so each needs one of the two.
3. Type your height and weight in the boxes for the units you picked.
4. Choose Show energy in calories (kcal) or kilojoules (kJ). One kcal is 4.184 kJ.
5. Read the big card for Mifflin-St Jeor, the second card for Harris-Benedict and the third for the gap. Use Copy result for a line of text or Copy link for a link that holds your numbers.

The two equations

The Mifflin-St Jeor equation comes from a 1990 paper in the American Journal of Clinical Nutrition by Mifflin, St Jeor and colleagues. They measured resting energy by indirect calorimetry in 498 healthy adults aged 19 to 78 and fitted a line through the results. The simplified form in the abstract is: resting energy = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5 for men, or − 161 for women.

The Harris-Benedict equations come from a 1918 paper by J Arthur Harris and Francis G Benedict in the Proceedings of the National Academy of Sciences. The printed equations give heat production per 24 hours, with weight in kilograms, stature in centimetres and age in years:

• Men: 66.4730 + 13.7516 × weight + 5.0033 × height − 6.7550 × age
• Women: 655.0955 + 9.5634 × weight + 1.8496 × height − 4.6756 × age

A revision by Roza and Shizgal followed in 1984. Its abstract says the equations hold up with extra subjects added, but it does not print the new coefficients, so this page does not use it and does not quote numbers for it.

Worked example: a woman, 30, 168 cm, 65 kg

Mifflin-St Jeor: 10 × 65 = 650, 6.25 × 168 = 1,050 and 5 × 30 = 150. So 650 + 1,050 − 150 − 161 = 1,389 calories a day.

Harris-Benedict: 9.5634 × 65 = 621.62, 1.8496 × 168 = 310.73 and 4.6756 × 30 = 140.27. So 655.0955 + 621.62 + 310.73 − 140.27 = 1,447 calories a day. That is 58 more than Mifflin-St Jeor, or 4.2% higher.

Worked example: a man, 35, 180 cm, 80 kg

Mifflin-St Jeor: 800 + 1,125 − 175 + 5 = 1,755 calories a day. Harris-Benedict: 66.4730 + 1,100.13 + 900.59 − 236.43 = 1,830.77, so 1,831. The gap is 76 calories, or 4.3%.

What changes the number

In the Mifflin-St Jeor equation each extra kilogram adds 10 calories a day, each extra centimetre adds 6.25 and each extra year of age takes away 5. The table below shows the 30 year old woman at 168 cm at four weights.

In Harris-Benedict a kilogram adds 9.56 calories for women and 13.75 for men, which is why the two equations drift apart at higher weights for men and stay closer for women.

How accurate is it

Both are estimates for a group, not a measurement of you. The Mifflin-St Jeor paper reported that the Harris-Benedict equations from 1919 overestimated the resting energy it measured by 5%. The 1984 Roza and Shizgal paper reported that the Harris-Benedict equations predict the resting energy of a normally nourished person with a precision of 14%. Real BMR also varies with muscle mass, which neither equation knows. A direct measurement needs indirect calorimetry in a clinic.

Common problems

• The yellow note about an age or height range means the equation was not fitted to people like that. Treat the number as rougher.
• A height that looks like metres or feet gets a hint instead of a result. Type centimetres, or switch the units.
• The result is for a full day at rest. Add your activity with the TDEE calculator, and see your weight band with the BMI calculator.

This page is maths, not medical advice. The two papers are linked below, checked 24 Oct 2026:

• Mifflin and others, Am J Clin Nutr 1990;51:241-7
• Harris and Benedict, PNAS 1918;4:370-373
• Roza and Shizgal, Am J Clin Nutr 1984;40:168-82