How to use this bmr calculator
Select the sex term used by the equation, enter age, and choose metric or US measurements. The original equation has separate male and female constants; choose the term your clinician or nutrition professional considers appropriate for this calculation. Enter current weight and height, then read the rounded daily estimate. Do not add an activity multiplier when the question asks specifically for BMR.
How the calculation works
The Mifflin–St Jeor equations were published in 1990 after researchers measured resting energy expenditure in 498 adults. The equation combines body mass, height, age, and a sex-specific constant. It predicts resting expenditure; it does not directly measure oxygen consumption or an individual's metabolism.
BMR and resting energy expenditure are often used interchangeably online, although laboratory protocols differ. Daily living requires more energy than resting metabolism because movement, work, exercise, digestion, temperature regulation, and recovery add expenditure. Use the separate Calorie Calculator for a transparent activity-multiplier estimate.
Formulas
Male equation term
Female equation term
Variables
Worked examples
Adult using the male equation
For age 35, 80 kg, and 180 cm: 10(80) + 6.25(180) − 5(35) + 5 = 1,755 kcal/day.
Adult using the female equation
For age 42, 65 kg, and 165 cm: 10(65) + 6.25(165) − 5(42) − 161 = approximately 1,310 kcal/day.
Common uses
Energy-planning baseline
Establish a transparent resting-energy estimate before considering activity. Keeping BMR separate from total expenditure prevents the activity assumption from disappearing inside one unexplained number.
Compare prediction methods
Use the displayed Mifflin–St Jeor result when comparing an app, wearable, or another published equation. Differences do not necessarily mean one device measured metabolism.
Educational examples
Explore how the equation changes as age, height, or weight changes while holding other inputs constant. This demonstrates the model without implying that intentional weight change follows a simple linear rule.
Accuracy and limitations
The implementation follows the published Mifflin–St Jeor coefficient structure and converts US measurements before calculation. It rounds the final estimate to the nearest kilocalorie per day.
A prediction equation estimates a group relationship. Individual resting expenditure can differ, and laboratory indirect calorimetry performed under a defined protocol is not equivalent to this browser calculation.
Sources and methodology
NumUtility uses the following primary or authoritative references for this calculator. Sources explain the method; they do not turn the result into personal medical advice.
Frequently asked questions
Is BMR the number of calories I should eat?
Not by itself. BMR estimates resting energy expenditure. Total daily needs also reflect movement, exercise, digestion, health status, and other individual factors.
Why does the formula ask for sex?
The published Mifflin–St Jeor equation uses two constants labelled male and female. That binary model is a limitation of the equation and does not capture every person's physiology.
Can a fitness tracker measure BMR?
Many devices estimate resting energy from profile data. A laboratory indirect-calorimetry assessment is different from a prediction equation or wearable estimate.
Why might my actual needs differ?
Body composition, health conditions, medications, temperature, recovery, pregnancy, and measurement error can all make real expenditure differ from a population equation.
Are my health measurements stored?
No. Calculations run in your browser. NumUtility does not receive or save the values you enter in these tools.