Mifflin–St Jeor
Men: 10W + 6.25H − 5A + 5
Women: 10W + 6.25H − 5A − 161
Resting calorie estimator
Basal Metabolic Rate Calculator
Estimate the calories your body may use at rest with Mifflin–St Jeor, revised Harris–Benedict, and—when body-fat percentage is available—a lean-mass equation.
Multiple recognized equations Calculation stays in your browser kcal/day resting estimate
Free BMR calculator
Estimate resting calorie expenditure
Enter your age, body size and equation coefficient set. Body-fat percentage is optional unless you choose the lean-mass equation.
Calculation methodology
How the BMR equations work
These equations predict resting energy from body measurements. They do not directly measure metabolism. True basal measurement requires tightly controlled laboratory conditions; in everyday fitness use, “BMR calculator” commonly refers to an estimated resting-energy value.
Revised Harris–Benedict
Men: 88.362 + 13.397W + 4.799H − 5.677A
Women: 447.593 + 9.247W + 3.098H − 4.330A
Cunningham 1991
REE: 370 + 21.6 × fat-free mass (kg)
Fat-free mass = weight × (1 − body-fat % ÷ 100).Understanding your result
What your BMR estimate means
The result approximates energy used to support essential functions at rest—such as circulation, breathing, temperature regulation and cellular activity. It is not a recommended food intake and does not include exercise or normal daily movement.
To estimate activity-inclusive maintenance calories, use BMR or resting energy as a starting point inside a TDEE calculation.
BMR / resting estimate
Calories predicted for basic resting energy needs.
TDEE
Resting energy plus movement, exercise and other daily expenditure.
Body composition
Lean mass can influence resting expenditure, which is why a body-fat-based equation may differ from weight-based equations.
Accuracy & limitations
Why predicted BMR can differ from measured metabolism
Prediction equations describe population averages. Individual metabolism can differ because of body composition, age, health status, medications, hormonal factors and measurement conditions.
Equation choice matters
Mifflin and revised Harris–Benedict use different datasets and coefficients, so small differences are expected.
Body-fat accuracy matters
The lean-mass equation is only as useful as the body-fat estimate used to derive fat-free mass.
Large individual error is possible
Even well-known equations can miss measured resting energy for an individual, especially at extremes of body size or in clinical conditions.
Indirect calorimetry is different
Laboratory indirect calorimetry measures gas exchange and can provide a more individualized resting-energy value when clinically appropriate.
Practical fitness use
How to use a BMR estimate responsibly
A BMR estimate is most useful as a baseline for understanding energy expenditure—not as a stand-alone calorie target. Your real daily needs include movement, training, digestion and day-to-day variability.
Start with a transparent equation
Use Mifflin–St Jeor as a practical default and compare Harris–Benedict to understand model spread.
Use measured body fat cautiously
If you have a credible body-fat estimate, compare the lean-mass equation rather than assuming it is automatically superior.
Move from BMR to TDEE
For maintenance-calorie planning, combine resting energy with realistic activity rather than eating at BMR by default.
Tool guide
Understand and use the BMR Calculator
Use these tool-specific notes to understand the method, enter better data, interpret the output, and apply the result appropriately.
Resting Energy
BMR/REE equations estimate the energy needed for basic physiological functions at rest. They predict resting expenditure; they do not include normal daily movement or exercise.
Choose an Equation
Mifflin–St Jeor is a practical general-adult default, revised Harris–Benedict offers another weight/height/age estimate, and Cunningham uses fat-free mass when a credible FFM value is available.
Inputs & Units
Enter measured weight, height, age, and the sex category required by the selected regression. Unit conversions occur before the equation so metric and imperial entries remain equivalent.
Use the Estimate
Use BMR as a starting point for energy planning, not as a calorie target by itself. Maintenance intake requires additional allowance for movement, exercise, and other components of total expenditure.
Frequently asked questions
BMR Calculator FAQs
Practical answers about this tool's inputs, method, results, limitations, and common real-world use.
What is BMR?
Basal metabolic rate describes the energy required to maintain essential physiological functions under strict resting conditions. Online equations provide a prediction rather than a direct measurement.
Which BMR formula should I use?
Mifflin–St Jeor is a practical default for many adults. Revised Harris–Benedict provides a useful comparison. If you have a credible body-fat estimate, the lean-mass equation gives an additional perspective.
Is BMR the same as resting metabolic rate?
They are related but not identical laboratory concepts. BMR requires stricter testing conditions. In fitness calculators, the terms are often used loosely for resting-energy predictions, so this page labels the result as an estimate.
Is BMR how many calories I should eat?
No. BMR excludes normal activity. Maintenance intake is closer to total daily energy expenditure, which adds movement and exercise to resting energy.
Why do formulas give different answers?
Each equation was derived from a different dataset and regression model. A modest spread is expected and is one reason results should not be treated as exact measurements.
When should I recalculate?
Recalculate after meaningful changes in body weight, age over time, or body composition. For everyday planning, small day-to-day weight fluctuations do not require a new BMR calculation.
Can body-fat percentage improve a BMR estimate?
It can enable a fat-free-mass equation such as Cunningham, but the result is only as reliable as the body-composition estimate. A poor body-fat measurement can introduce more error rather than less.
Why does BMR usually fall during weight loss?
A smaller body generally requires less energy at rest, and changes in fat-free mass can also affect resting expenditure. Adaptive changes can occur too, so equations remain estimates rather than measurements.
Do metric and imperial inputs change the equation?
No. Imperial values are converted to the units required by the selected formula before calculation. The same person should receive the same estimate regardless of the unit system used.
Can I use BMR to set a minimum food intake?
Not as a universal rule. BMR is a resting-energy prediction, not a personalized safety threshold or nutrition prescription. Appropriate intake depends on total needs, goals, health, and clinical context.
Method & references
Evidence behind the calculator
The default equation comes from Mifflin and colleagues; the revised Harris–Benedict coefficients come from Roza and Shizgal. The optional fat-free-mass equation is included as a comparison when body composition is available.
- Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. American Journal of Clinical Nutrition, 1984.
- Recent clinical-trial analysis describing the 370 + 21.6 × lean body mass resting-energy equation.
- Fitness Goal 4U TDEE Calculator: activity-inclusive daily calorie estimation.
Content reviewed: .
Health and nutrition disclaimer
This calculator is an educational estimate, not a medical diagnosis or calorie prescription. Energy needs can differ substantially during pregnancy, adolescence, illness, eating-disorder recovery, high-level sport, or when medications and medical conditions affect metabolism. If your nutrition needs are medically complex, consult a qualified healthcare professional or registered dietitian.