Health Calculators
BMR Calculator
BMR is the energy your body spends at complete rest, before any activity: breathing, circulation, temperature control. Enter your sex, age, height and weight and this calculator returns it in kcal/day and kJ/day with Mifflin-St Jeor, the equation most dietitians use, beside three older estimates. It is a population average, not a measurement.
Formula Used
BMR (kcal/day) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5 for men and − 161 for women (Mifflin-St Jeor). Katch-McArdle instead uses BMR = 370 + 21.6 × lean body mass (kg).
About This Calculator
What It Does
Calculate your basal metabolic rate — the energy your body uses when completely at rest — from your sex, age, height and weight. The page returns Mifflin-St Jeor as the headline value and shows Harris-Benedict (revised) and Schofield beside it, plus Katch-McArdle when you supply a body-fat percentage, in kcal/day and kJ/day. Seeing the four together is the point: for one adult they disagree by a few hundred kilocalories, which is how far a population estimate can be from an individual.
Worked Example
A 30-year-old man, 180 cm and 80 kg. Mifflin-St Jeor: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 kcal/day. Revised Harris-Benedict: 88.362 + 13.397 × 80 + 4.799 × 180 − 5.677 × 30 = 1,854 kcal/day. Schofield for a 30-year-old: 11.472 × 80 + 873.1 = 1,791 kcal/day. At 15 % body fat his lean mass is 80 × 0.85 = 68 kg, and Katch-McArdle gives 370 + 21.6 × 68 = 1,839 kcal/day. The four answers span 74 kcal/day, and this resting figure is still only 60-75 % of what he burns on an active day.
Real-World Usage
BMR anchors every calorie target that follows it. A dietitian multiplies it by an activity factor to size a maintenance intake and then adjusts for a weight-loss or weight-gain goal. Gyms use the same number to set calorie and protein floors, and hospital teams use a BMR estimate to plan feeding for a patient on bed rest. Because the estimates disagree, the useful comparison is with yourself over time: recalculate after about 5 kg of weight change rather than after a weekend.
Local Context
Every equation here was fitted on North American or European adults and is used worldwide without local adjustment; no country publishes its own BMR constants. The practical difference is units: most of continental Europe and Latin America record height in centimetres and weight in kilograms, while the United States and Canada still use feet, inches and pounds. Food labels follow the same split — kilocalories on a US label, kilojoules on a European one, which is why this page reports both.
BMR Is Not Your Daily Burn
BMR is what you would spend lying still for 24 hours. Almost nobody lives there: walking, working, training and even digesting food add 25-40 % on top. The step from BMR to a daily target is an activity multiplier — about 1.2 for a desk-bound day and up to 1.9 for heavy training on top of manual work — and that product is your total daily energy expenditure. Use this page for the resting floor and the TDEE calculator for the day's total.
Where the Estimates Fall Short
Mifflin-St Jeor was fitted on normal-weight and overweight adults and is the most accurate of the four for most people, but every equation here is a population average with a standard error of roughly ±150-350 kcal/day. They read high for people carrying a lot of lean mass, such as athletes and some manual workers, and low for people with obesity, and none of them accounts for thyroid disease, medication, pregnancy, fever or a very low-calorie diet. Treat a single number as a starting point to check against two or three weeks of real weight change, not as a measurement.
BMR and RMR Are Not the Same Test
BMR is measured under strict conditions: complete rest, thermal comfort, no food for several hours, often just after waking. Resting metabolic rate is measured under looser ones and includes the energy used to digest food, so it comes out a few per cent higher. Most BMR calculators, including the equations on this page, actually estimate resting expenditure — the gap is small enough that the two numbers are used interchangeably day to day.
Sources and Methodology
Mifflin MD, St Jeor ST, et al. 'A new predictive equation for resting energy expenditure in healthy individuals.' American Journal of Clinical Nutrition, 1990. Roza AM, Shizgal HM. 'The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass.' American Journal of Clinical Nutrition, 1984. Schofield WN. 'Predicting basal metabolic rate, new standards and review of previous work.' Human Nutrition: Clinical Nutrition, 1985 — the weight-only equations adopted by the FAO/WHO/UNU. Katch FI, McArdle WD, Katch VL. 'Exercise Physiology: Energy, Nutrition and Human Performance' — the lean-mass equation BMR = 370 + 21.6 × lean mass. Energy conversion at 1 kcal = 4.184 kJ.
Last reviewed: September 2026.
Frequently Asked Questions
What is BMR?
Basal metabolic rate is the energy your body uses at complete rest just to stay alive: breathing, heart rate, body temperature and brain activity. It is usually between 60 % and 75 % of the energy a person spends in a day.
Is my BMR the number of calories I need each day?
No. BMR is the resting floor only. Your daily need is BMR multiplied by an activity factor of roughly 1.2 to 1.9, which gives your total daily energy expenditure.
Which BMR formula should I use?
Mifflin-St Jeor is the best general choice for adults and is the one this page leads with. Katch-McArdle is better when you know your body-fat percentage, because it works from lean mass. Harris-Benedict and Schofield are older population estimates.
Why does BMR fall with age?
Mostly because lean mass falls as we get older: muscle and organs are the metabolically active tissue, and fat burns far less energy per kilogram. Every equation here carries age as a term, but the individual spread is wide.
What is the difference between BMR and RMR?
Resting metabolic rate is measured under looser conditions and includes the energy used to digest food, so it reads a few per cent higher than BMR. Day to day the two describe the same resting floor.