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- Basal metabolic rate (BMR) is the energy your body uses at complete rest to keep you alive, for things like breathing, circulation and cell repair.
- This calculator uses the Mifflin-St Jeor equation as the main result and shows the revised Harris-Benedict equation for comparison.
- Multiplying BMR by an activity factor gives an estimate of the calories you use over a whole day.
- The results are estimates for adults. This page is general information, not medical advice.
How to use the BMR calculator
Choose your sex and enter your age
The equations use different constants for men and women, and they take age into account.
Choose units and enter height and weight
Use metric or US units, whichever you know.
Pick your activity level
Choose the one that matches a normal week. Most people overestimate how active they are, so be honest.
Read the results
You get BMR from both formulas, plus daily calorie needs for your level and for every level.
The BMR formulas
Mifflin-St Jeor equation
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Daily needs = BMR × activity factor
The result is in calories per day, meaning kilocalories, the unit on food labels.
The revised Harris-Benedict equation uses the same inputs with different constants. For men it is 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age, and for women it is 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age. Mifflin-St Jeor was published in 1990 and is widely used for modern adults. Both are estimates, so the calculator shows both and lets you see how far apart they are.
Activity levels
Activity factors
The multiplier applied to BMR for daily calorie needs.
These factors are rough averages. Real daily energy use varies from person to person.
Worked examples
Example 1: a 30-year-old man
He is 170 cm tall, weighs 70 kg and has a light activity level.
The two formulas differ by about 54 calories here, which is small next to the daily total.
Example 2: a 28-year-old woman
She is 165 cm tall, weighs 60 kg and has a sedentary activity level.
Here the formulas differ by 62 calories.
Example 3: every activity level
The same 30-year-old man, using Mifflin-St Jeor.
Only one row describes a typical week, so pick the honest one.
What affects your metabolism
Muscle burns more energy than fat at rest, so people with more muscle tend to have a higher BMR at the same weight. BMR usually falls slowly with age and is generally higher in larger bodies. It can also be affected by thyroid conditions, some medicines, illness, pregnancy and extreme dieting. The equations know none of these things, so treat the result as a starting estimate rather than an exact measurement.
Where a BMR calculator helps
Understanding energy needs
See roughly how many calories your body uses in a day.
Meal planning
Use the daily estimate as a reference when you plan meals with a professional.
Fitness plans
Compare how different activity levels change your daily needs.
Health conversations
Bring a clear number to a doctor or dietitian.
Check your weight status with the BMI calculator, compare formulas with the ideal weight calculator, or estimate protein with the protein intake calculator. This page is general information and not medical advice. Please talk to a doctor or registered dietitian before making big changes to what you eat, especially if you are pregnant, ill or under 18.
BMR calculator FAQ
What is BMR?
BMR is the number of calories your body burns at rest over a day to keep basic functions running, such as breathing and circulation.
Which BMR formula is more accurate?
Mifflin-St Jeor is widely used for modern adults, and the revised Harris-Benedict equation is an older alternative. Both are estimates, so the calculator shows both.
What is the difference between BMR and daily calorie needs?
BMR is the energy used at rest. Daily needs add the energy used for movement, exercise and digesting food, which the calculator estimates by multiplying BMR by an activity factor.
Should I eat my BMR number of calories?
The number is an estimate of what your body uses at rest, not a diet target. Eating far below your needs can be unsafe, so talk to a doctor or dietitian before changing how you eat.
Why do men and women get different results?
On average, men have more muscle and larger bodies at the same height and weight, so the equations use a different constant for each sex. Individual people vary a lot.
Does BMR change over time?
Yes. It changes with weight, muscle, age and health, so calculate it again when those change.