BMR Calculator
Estimate how much energy your body uses at rest, compare three established equations and see how activity changes your estimated total daily energy expenditure.
Your details
Enter your details to estimate resting energy expenditure.
Add this only if you have a reasonable estimate. It enables the lean-mass-based Katch–McArdle comparison.
Your BMR estimate will appear here
Enter your age, sex, height and weight. Body fat is optional and is only needed for the Katch–McArdle comparison.
Mifflin–St Jeor estimate. This is an equation-based estimate of energy use at rest, not a laboratory measurement or a calorie intake recommendation.
Compare formulas
Estimates can differOptional activity adjustment. This is separate from BMR and remains an estimate.
activity factor
BMR estimates resting energy. Activity-adjusted expenditure adds an activity factor to give a broader daily estimate.
Prediction equations make different assumptions. Comparing them makes that uncertainty visible instead of presenting one estimate as exact.
What does BMR actually mean?
Basal metabolic rate describes the energy your body needs to maintain essential functions while at rest — things such as breathing, circulation and normal cellular activity.
In a laboratory, true BMR is measured under tightly controlled conditions. Online calculators cannot measure your metabolism directly, so they use prediction equations based on characteristics such as weight, height, age and sex.
Basal metabolic rate is defined under stricter conditions, including rest, fasting and a thermoneutral environment.
Resting metabolic rate or resting energy expenditure also describes energy use at rest, but measurement conditions are generally less restrictive than for BMR.
Total daily energy expenditure goes beyond resting needs by also accounting for activity and other components of daily energy use.
BMR is the term most people recognise when searching for this type of calculator. Technically, equations such as Mifflin–St Jeor were developed to predict resting energy expenditure. CalcNest labels the result clearly so an equation-based estimate is not confused with a laboratory measurement.
Which BMR formulas does CalcNest use?
The calculator shows several established prediction equations rather than hiding the fact that different methods can produce different estimates.
W is weight in kilograms, H is height in centimetres and A is age in years. The equation was developed from measured resting energy expenditure in 498 adults and is used as CalcNest's main estimate.
This is the Roza–Shizgal reevaluation of the Harris–Benedict approach. It uses age, height, weight and sex but different coefficients from Mifflin–St Jeor.
This method uses estimated lean body mass instead of age, height and a sex-specific constant. Its usefulness therefore depends heavily on the quality of the body-fat percentage entered.
Different equations use different coefficients, but their predicted values can cross or converge for a particular combination of age, height and weight. Similar results for one person do not mean the equations are mathematically identical.
BMR calculation example
Take a 30-year-old male who weighs 80 kg and is 180 cm tall. Using the Mifflin–St Jeor equation:
This is a predicted resting-energy value. It does not mean this person should consume exactly 1,780 calories per day.
What affects resting energy expenditure?
Prediction equations simplify a complex biological process. Some of the differences between people are represented by the calculator's inputs, while others are not.
Larger bodies generally require more energy to maintain their tissues at rest.
Lean and fat mass contribute differently to energy expenditure, which is why lean-mass-based equations can produce another estimate.
Age is included directly in Mifflin–St Jeor and Revised Harris–Benedict prediction equations.
An equation cannot capture every physiological difference between people, so the result should be treated as an estimate.
BMR is not the same as your daily calorie needs
Your body uses energy for more than basic resting functions. Movement, planned exercise, digestion and other activity contribute to total daily energy expenditure.
The activity selector in the calculator multiplies the primary resting-energy estimate by a commonly used activity factor. That makes the TDEE figure a broader estimate, but it does not turn it into an exact measurement.
Activity categories are especially easy to over- or underestimate. Two people who both describe themselves as “moderately active” may have very different jobs, step counts, training loads and daily routines.
BMR estimates resting energy expenditure. The activity-adjusted TDEE estimate is intended to give broader context for total daily energy use. Neither result is a personalised dietary prescription.
When can a BMR calculator be less reliable?
Prediction equations are useful for estimates, but they are not a substitute for measuring resting energy expenditure or obtaining individual clinical advice.
Height-and-weight equations cannot directly see how body weight is divided between different tissues.
Katch–McArdle depends on the body-fat value entered. An inaccurate body-fat estimate produces an inaccurate lean-mass estimate.
This CalcNest tool is designed for adults aged 18 and over rather than paediatric energy assessment.
Pregnancy, illness, medications and other circumstances can make a general adult prediction tool inappropriate for individual decisions.
If you need an energy estimate because of a medical condition, pregnancy, an eating disorder, significant weight change or another health concern, seek advice from an appropriately qualified health professional rather than relying on a general calculator.
How we calculate and present your result
CalcNest performs the equations directly in your browser. Metric inputs are used by the formulas; imperial height and weight are converted to centimetres and kilograms before calculation.
Mifflin–St Jeor is displayed as the primary resting-energy estimate. Revised Harris–Benedict is shown alongside it so you can see that prediction methods may differ. Katch–McArdle appears when body-fat percentage is supplied.
Results are rounded for readability. The calculator does not use AI to alter the deterministic formula outputs.
Mifflin MD, St Jeor ST, Hill LA, et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals . American Journal of Clinical Nutrition.
Roza AM, Shizgal HM (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass . American Journal of Clinical Nutrition.
Definitions of BMR and RMR were cross-checked against published clinical literature describing basal and resting energy expenditure.
BMR calculator FAQs
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