BMR Calculator
Find your Basal Metabolic Rate — the calories your body burns at complete rest — with Mifflin-St Jeor, Harris-Benedict, Katch-McArdle and four other equations side by side, plus your daily calories at six activity levels.
How it works
Mifflin-St Jeor: BMR = 10×kg + 6.25×cm − 5×age + 5 (men) / − 161 (women) · Revised Harris-Benedict: men 88.362 + 13.397×kg + 4.799×cm − 5.677×age, women 447.593 + 9.247×kg + 3.098×cm − 4.330×age · Katch-McArdle: 370 + 21.6×LBM · Cunningham: 500 + 22×LBM (LBM = lean body mass in kg)
Basal metabolic rate is the energy your body uses for breathing, circulation, temperature and cell repair before any movement or digestion. The calculator runs seven published equations on your numbers and lets you pick which one leads. Mifflin-St Jeor (1990) is the default because validation studies found it the closest to measured rates for most adults, usually within about 10%. The Harris-Benedict equation is shown in both its 1984 revision (Roza and Shizgal) and its original 1919 form, which tends to read high. Katch-McArdle and Cunningham ignore sex and age and work from lean body mass — weight minus fat — so they suit lean or muscular people who know their body fat percentage; leave body fat at 0 and lean mass is estimated with the Boer formula. Schofield, used by the WHO, needs only weight in age bands, and Owen uses weight alone. US units are converted first (1 lb = 0.4536 kg, 1 in = 2.54 cm), and 1 kcal = 4.184 kJ. The activity table multiplies BMR by the usual factors from 1.2 (sedentary) to 1.9 (extra active) to estimate total daily burn.
Worked example
A 30-year-old man, 5′9″ (175.26 cm) and 170 lb (77.11 kg): Mifflin-St Jeor gives 10×77.11 + 6.25×175.26 − 5×30 + 5 = 1,721 kcal/day (7,203 kJ), or about 72 kcal an hour. The revised Harris-Benedict equation gives 1,792 kcal and the original 1919 version 1,801. If he has 18% body fat, his lean mass is 63.2 kg and Katch-McArdle gives 370 + 21.6×63.2 = 1,736 kcal. At light activity (×1.375) he burns about 2,367 kcal a day.
Sources: Mifflin MD et al. (1990) — A new predictive equation for resting energy expenditure · Roza AM, Shizgal HM (1984) — The Harris Benedict equation reevaluated · Frankenfield D et al. (2005) — Comparison of predictive equations for resting metabolic rate · FAO/WHO/UNU — Human energy requirements (Schofield equations)
Frequently asked questions
BMR vs TDEE — what’s the difference?
BMR is the energy you burn lying completely still. TDEE (total daily energy expenditure) multiplies it by your activity level to estimate what you really burn in a day, and it is the number diet planning uses. The activity table under the result gives that figure for six activity levels.
Which BMR equation should I use?
For most adults, Mifflin-St Jeor. If you are lean or muscular and know your body fat percentage from a reliable method, Katch-McArdle or Cunningham can be closer because muscle burns more energy than fat. Schofield is the WHO equation and works when only weight is known. The table shows all seven so you can see how much they agree.
Can I eat below my BMR?
Sustained intakes far below BMR are hard to keep up and can cost muscle and nutrients. Weight-loss targets are normally set from TDEE, not BMR, kept moderate, and kept at or above about 1,200 kcal a day for women and 1,500 for men unless a doctor is supervising.
Why do results differ between BMR calculators?
They use different equations built from different groups of people. Mifflin-St Jeor and the revised Harris-Benedict usually land within 5% of each other; all of them are estimates within roughly ±10% for an individual. Only a lab test (indirect calorimetry) measures your own rate.
Why does BMR drop with age?
People tend to lose muscle and some organ energy use with age. Mifflin-St Jeor takes off 5 kcal a day for each year, so the same person burns about 150 kcal less at 60 than at 30. Strength training slows that loss.
Related calculators
This is a general educational estimate, not medical advice. Bodies differ — for decisions about diet, training, medication or health conditions, talk to a doctor or registered dietitian.