BMR Calculator
Estimate your basal metabolic rate, the calories your body burns at rest.
A BMR calculator estimates basal metabolic rate, which is the energy your body uses at rest to support basic functions such as breathing, circulation, temperature regulation, and cellular activity. This calculator uses the Mifflin–St Jeor equation for the main result, based on sex, age, height in centimeters, and weight in kilograms. It also shows the Revised Harris–Benedict estimate plus two simple activity-based reference rows.
That makes the tool useful as a starting point for meal planning, weight-management discussions, or understanding the phrase how many calories does my body burn at rest. Still, BMR is not the same thing as everything you burn in a typical day. Walking, exercise, digestion, work activity, and day-to-day movement all sit on top of resting energy needs, so the estimate is a baseline rather than a personal rule.
How to use the BMR Calculator
- Choose "Sex" first because the equation uses a different constant for males and females in the main Mifflin–St Jeor result.
- Enter "Age", "Height", and "Weight" in the units requested by the calculator. The math depends directly on those three values, so accurate measurements improve the estimate.
- Read the main "Basal metabolic rate" line as the calories your body burns at rest each day according to the implemented formula.
- Review the supporting rows for "Mifflin–St Jeor" and "Revised Harris–Benedict". They are separate predictive equations, so a difference between them is normal.
- Use the "Sedentary" and "Moderate" rows as simple reference points for broader daily energy needs. They multiply the resting estimate by standard activity factors and should be treated as planning ranges, not prescriptions.
Formula
BMR = 10W + 6.25H − 5A + s (Mifflin–St Jeor)
Example: using the BMR calculator for a daily baseline
Suppose "Sex" is Female, "Age" is 34, "Height" is 165 cm, and "Weight" is 62 kg. With those inputs, the calculator returns a "Basal metabolic rate" of 1,320 kcal/day. It also shows "Mifflin–St Jeor" as 1,320 kcal, "Revised Harris–Benedict" as 1,385 kcal, "Sedentary (×1.2)" as 1,584 kcal, and "Moderate (×1.55)" as 2,046 kcal.
The main result comes from the Mifflin–St Jeor equation used in the code: 10 times weight plus 6.25 times height minus 5 times age minus 161 for females. With these values, that is 10 × 62 + 6.25 × 165 − 5 × 34 − 161, which equals 620 + 1,031.25 − 170 − 161 = 1,320.25. The calculator rounds that to 1,320 kcal/day. The higher activity rows are then derived by multiplying that BMR by 1.2 and 1.55, which is why they display 1,584 and 2,046 kcal.
How to interpret the result
The most useful way to read a bmr calculator is as a baseline estimate rather than a target to follow rigidly. A result near 1,320 kcal/day in this example does not mean a person should eat only that amount. It means the formula estimates that level of energy use at rest before normal daily activity is added.
The Mifflin St Jeor calculator row and the Revised Harris–Benedict row can differ because predictive equations are built from different research models. That variation is a reminder that metabolism estimates are approximate.
If your real-world weight trend and energy intake do not line up with the estimate, the number should be adjusted in light of actual outcomes, routine, and health context.
Next, you may also find these useful: BMI Calculator, Calorie Calculator, Body Fat Calculator.
Assumptions and limitations
- This calculator uses the Mifflin–St Jeor equation for the main BMR result and also shows a Revised Harris–Benedict estimate for comparison. Both are predictive equations, not direct metabolic measurements.
- The output assumes adult users and relies on entered height and weight values being reasonably accurate. Rough guesses can make the estimate less useful.
- The activity rows are simple multipliers applied to BMR. Real total daily energy expenditure can differ because of occupation, exercise volume, body composition, medications, illness, or metabolic adaptation.
- The result does not replace clinical evaluation, indirect calorimetry, or individualized nutrition advice. Pregnancy, breastfeeding, growth, recovery from illness, and athletic performance goals may require more specialized assessment.
Frequently asked questions
What is the difference between a BMR calculator and a calorie calculator?
A BMR calculator focuses on resting energy needs only. A broader calorie calculator usually starts with BMR and adds an activity factor to estimate total daily needs. BMR is the foundation, not the whole picture.
Why does the Mifflin St Jeor calculator matter so much online?
Mifflin–St Jeor is widely used because it gives a practical resting-energy estimate from simple body measurements. It is not perfect, but it is often used as a reasonable starting equation in nutrition and weight-management planning.
Does BMR tell me exactly how many calories my body burns at rest?
No. It estimates resting energy expenditure from a formula. Sleep, stress, body composition, hormones, illness, medications, and measurement error can all shift real energy use above or below the predicted number.
Why are there two equation rows in the results?
They show that more than one predictive formula exists. If the Mifflin–St Jeor and Revised Harris–Benedict estimates are close, that can increase confidence that your baseline is in the right range.
Should I eat at my BMR if I want to lose weight?
Not automatically. BMR reflects resting needs, not full daily needs, so eating at or below that level may be unnecessarily aggressive for some people. Sustainable calorie targets should consider daily activity, health status, and professional guidance when needed.
When should I get professional advice instead of relying on a BMR calculator?
It is wise to seek individualized advice if you have a medical condition, a history of disordered eating, unusual weight change, pregnancy, breastfeeding, or a serious athletic goal. In those cases, a clinician or registered dietitian can interpret the estimate in context.
Sources and further reading
- National Institute of Diabetes and Digestive and Kidney Diseases: Body Weight Planner
- National Heart, Lung, and Blood Institute: Aim for a Healthy Weight
- MedlinePlus: Metabolism
Last reviewed: 2026-10-02. See our editorial policy.
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Health information is general and not a diagnosis or medical advice. Consult a qualified professional. Full disclaimer