What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to keep essential functions running, such as breathing, circulating blood, regulating body temperature, and repairing cells. It represents the minimum amount of energy you would expend in a day if you simply lay still and did nothing else.
BMR is reported in kilocalories per day (kcal/day) and forms the foundation of any calorie-planning effort. Because resting metabolism accounts for the majority of most people’s daily energy expenditure, knowing your BMR is the first step toward estimating how much you should eat to lose, maintain, or gain weight.
The Mifflin-St Jeor equation
This calculator uses the Mifflin-St Jeor equation, published in 1990, which is widely regarded as one of the most accurate predictive formulas for resting energy expenditure in healthy adults. It improved on the older Harris-Benedict equation by better reflecting modern body compositions.
The equation takes four inputs: sex, weight (in kilograms), height (in centimeters), and age (in years). A constant term differs between men and women to account for typical differences in lean body mass.
Formula
The Mifflin-St Jeor equation calculates BMR as follows, with weight in kilograms, height in centimeters, and age in years:
-
For men:
-
For women:
The only difference between the two formulas is the final constant: men add 5, while women subtract 161. The calculator converts any weight or height units you enter into kilograms and centimeters before applying the equation.
Examples
Example 1: BMR for a man
Suppose a man weighs 80 kilograms, is 180 centimeters tall, and is 30 years old.
His estimated BMR is approximately 1780 kcal/day.
Example 2: BMR for a woman
Suppose a woman weighs 60 kilograms, is 165 centimeters tall, and is 30 years old.
Her estimated BMR is approximately 1320.25 kcal/day.
Notes
- BMR is not the same as total daily calories. To estimate how many calories you actually burn, multiply your BMR by an activity factor that reflects how active you are. The calorie calculator does this for you.
- Estimates vary between individuals. Two people with identical sex, height, weight, and age can have different real metabolic rates because of muscle mass, genetics, hormones, and other factors.
- Designed for adults. Predictive equations like Mifflin-St Jeor are validated for adults and are less reliable for children, athletes with very high muscle mass, or people with certain medical conditions.
FAQs
What is the difference between BMR and TDEE?
BMR is the energy your body needs at complete rest. Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor, so it also includes the calories you burn through movement, exercise, and digestion.
Why does the formula differ for men and women?
On average, men carry more lean muscle mass than women of the same height and weight, and muscle burns more energy at rest. The different constant terms (+5 versus -161) adjust the estimate to reflect this typical difference in body composition.
How accurate is the Mifflin-St Jeor equation?
For most healthy adults, it estimates resting energy expenditure within roughly 10% of measured values, which is why dietitians and researchers commonly recommend it over older formulas. It remains an estimate, not a measurement.
Should I eat exactly my BMR in calories?
No. Eating only your BMR would generally be too few calories because it ignores the energy you spend on daily activity. Use your BMR as a baseline and add an activity factor to estimate a more realistic intake.
How is BMR related to BMI?
They answer different questions. BMR estimates how many calories you burn at rest, while BMI classifies your weight relative to your height. Both use weight and height, but BMR also depends on age and sex.