BMR CalculatorFree online fitness & health calculator — instant results, no sign-up
Basal metabolic rate with Mifflin-St Jeor and Harris-Benedict.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
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How the result changes with age
Each row below was calculated with this tool, keeping every other input at its default and changing only age from half to one and a half times the default value. Use it to see how sensitive the answer is before you enter your own numbers.
| Age (years) | Mifflin-St Jeor | Revised Harris-Benedict |
|---|---|---|
| 15 | 1,774 kcal/day | 1,848 kcal/day |
| 23 | 1,734 kcal/day | 1,802 kcal/day |
| 30 (default) | 1,699 kcal/day | 1,763 kcal/day |
| 38 | 1,659 kcal/day | 1,717 kcal/day |
| 45 | 1,624 kcal/day | 1,677 kcal/day |
About the BMR Calculator
This calculator estimates your Basal Metabolic Rate (BMR), the minimum daily calorie expenditure required to sustain vital physiological functions at complete rest. It provides side-by-side estimates using both the Mifflin-St Jeor equation and the Revised Harris-Benedict equation. Individuals use these estimates to establish baseline energy needs before factoring in physical activity for weight maintenance, loss, or gain.
- Age
- Chronological age in full years, typically between 15 and 100.
- Sex
- Biological sex (Male or Female), which determines the base physiological coefficients.
- Height
- Stature measured in centimeters (cm), typically between 100 and 250 cm.
- Weight
- Current total body mass measured in kilograms (kg), typically between 30 and 250 kg.
Formula and method
Mifflin-St Jeor: For Males: BMR = (10 × W) + (6.25 × H) − (5 × A) + 5 For Females: BMR = (10 × W) + (6.25 × H) − (5 × A) − 161 Revised Harris-Benedict (Roza and Shizgal, 1984): For Males: BMR = (13.397 × W) + (4.799 × H) − (5.677 × A) + 88.362 For Females: BMR = (9.247 × W) + (3.098 × H) − (4.330 × A) + 447.593
- BMRBasal metabolic rate in kilocalories per day (kcal/day)
- WBody weight in kilograms (kg)
- HHeight in centimeters (cm)
- AAge in years
The calculator takes biological sex, age, height, and weight to evaluate both the standard Mifflin-St Jeor equation and the 1984 Revised Harris-Benedict equation. Each raw result is rounded to the nearest integer and presented as daily kilocalories (kcal/day).
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Age30 years
- SexMale
- Height175 cm
- Weight75 kg
Results
- Mifflin-St Jeor1,699 kcal/day
- Revised Harris-Benedict1,763 kcal/day
How to use the BMR Calculator
- 1Select your biological sex to establish the baseline constant and variable coefficients.
- 2Multiply your weight in kilograms and height in centimeters by their respective formula multipliers.
- 3Multiply your age in years by the age multiplier and subtract it from the previous sum.
- 4Add or subtract the sex-specific constant and round to the nearest whole calorie.
Reading your result
The two figures represent the energy burned if you were to stay in bed resting all day in a thermoneutral environment. Mifflin-St Jeor is generally considered the closer baseline estimate for modern sedentary populations, while the Revised Harris-Benedict formula often trends slightly higher. To find total daily energy expenditure (TDEE), these values must be multiplied by an activity factor.
Limitations
These equations estimate metabolic rate based on total body weight rather than lean body mass. Consequently, they may overestimate energy expenditure in individuals with high body fat percentages and underestimate it in muscular athletes. They also do not reflect thyroid function, illness, ambient temperature, or metabolic adaptation from prolonged dieting.
Common questions
Why do the Mifflin-St Jeor and Revised Harris-Benedict results differ?+
They were derived from different population cohorts at different times. The Harris-Benedict formula (originally 1919, revised in 1984) often predicts slightly higher values, whereas Mifflin-St Jeor (developed in 1990) generally aligns closer to modern metabolic measurement studies.
Is BMR the total number of calories I burn in a day?+
No. BMR accounts only for basal life-support functions like breathing, circulation, and cell production. It does not include the thermic effect of food (digestion) or physical activity (walking, working, exercising).
Can I eat fewer calories than my BMR to lose weight faster?+
Eating below your BMR for extended periods can cause fatigue, nutrient deficiencies, and muscle loss. Most nutrition guidelines recommend establishing a deficit from your total daily energy expenditure (TDEE) rather than dropping below your basal rate.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.