About this BMR Calculator
Basal metabolic rate is the energy estimate for keeping the body functioning at rest, before deliberate exercise and most day-to-day movement are added.
The BMR Calculator in this script uses the Mifflin-St Jeor equations already shown on the health pages: weight, height, age, and sex are combined to estimate daily resting energy use.
That makes BMR a useful baseline when building a calorie plan, but it is not the same as the calories someone should eat each day. Total Daily Energy Expenditure is obtained only after activity is accounted for, usually by multiplying BMR by an activity factor.
The distinction matters because a person can have a BMR near 1,600 calories while maintaining weight at a much higher intake due to work, walking, training, and other activity. The result is an equation-based estimate rather than a metabolic-chamber measurement, so it is best used as a consistent planning reference.
What Is a BMR Calculator?
A BMR Calculator estimates basal metabolic rate: the approximate number of calories the body would use over a day to support essential processes such as breathing, circulation, temperature regulation, and organ function while at rest. The script uses the Mifflin-St Jeor method.
For men it applies BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women it uses the same weight, height, and age terms but subtracts 161 instead of adding 5. The answer is expressed as calories per day.
It is a baseline energy estimate, not an exercise target and not a direct measurement of an individual's metabolism.
Reading Your Results
Your result shows two distinct numbers that serve different purposes: your BMR, which represents the absolute minimum energy your body needs even if you stayed in bed all day, and your TDEE, which is the realistic total you actually burn once daily activity is factored in.
Most people should focus on the TDEE figure when setting a calorie target, since it reflects real-world energy expenditure rather than a theoretical baseline.
If your goal is fat loss, a common starting point is eating 300 to 500 calories below your TDEE, while a lean muscle-building goal often starts with a surplus of roughly 200 to 300 calories above it.
The BMR figure is still useful context, since it shows how much of your total burn comes from simply existing versus from movement, which can help explain why extreme calorie restriction often backfires by pushing intake too close to, or even below, your basic survival needs.
How to use this calculator
The calculator determines your Basal Metabolic Rate (BMR) and your Total Daily Energy Expenditure (TDEE).
Basal Metabolic Rate (Mifflin-St Jeor)
Total Daily Energy Expenditure
Activity Factors
Where
Example
Male BMR by Age (Estimated Calories/Day)
| Age (Years) | Average Height | Average Weight | Estimated BMR |
|---|---|---|---|
| 18–24 | 178 cm (5'10") | 72 kg | 1,760 kcal |
| 25–34 | 177 cm (5'10") | 76 kg | 1,720 kcal |
| 35–44 | 176 cm (5'9") | 80 kg | 1,680 kcal |
| 45–54 | 175 cm (5'9") | 81 kg | 1,640 kcal |
| 55–64 | 174 cm (5'8") | 79 kg | 1,590 kcal |
| 65–74 | 173 cm (5'8") | 76 kg | 1,530 kcal |
| 75+ | 172 cm (5'8") | 73 kg | 1,460 kcal |
Estimates based on average height and weight for each age group — your exact BMR depends on your own measurements.
Female BMR by Age (Estimated Calories/Day)
| Age (Years) | Average Height | Average Weight | Estimated BMR |
|---|---|---|---|
| 18–24 | 165 cm (5'5") | 60 kg | 1,430 kcal |
| 25–34 | 164 cm (5'4") | 64 kg | 1,390 kcal |
| 35–44 | 163 cm (5'4") | 67 kg | 1,350 kcal |
| 45–54 | 162 cm (5'4") | 68 kg | 1,310 kcal |
| 55–64 | 161 cm (5'3") | 66 kg | 1,260 kcal |
| 65–74 | 160 cm (5'3") | 63 kg | 1,220 kcal |
| 75+ | 159 cm (5'2") | 60 kg | 1,170 kcal |
Estimates based on average height and weight for each age group — your exact BMR depends on your own measurements.
Estimated Daily Calorie Needs by Activity Level
| Activity Level | Men | Women |
|---|---|---|
| Sedentary | 2,000–2,400 kcal | 1,600–2,000 kcal |
| Lightly Active | 2,200–2,600 kcal | 1,800–2,200 kcal |
| Moderately Active | 2,400–2,900 kcal | 2,000–2,400 kcal |
| Very Active | 2,800–3,300 kcal | 2,400–2,800 kcal |
| Extra Active | 3,200–3,800 kcal | 2,800–3,200 kcal |
Ranges reflect typical adult calorie needs by activity level — use your BMR result above alongside your own activity level for a more precise target.
Factors Affecting Your BMR Result
Weight and height raise the calculated BMR because larger bodies generally require more energy at rest under the equation. Age lowers the estimate through the five-calorie-per-year term, while the sex-specific constant creates a different equation branch.
Unit accuracy is critical: the formula expects kilograms and centimeters, so entering pounds or meters without conversion will produce a meaningless result.
The equation does not directly measure muscle mass, thyroid function, fever, pregnancy, medications, hormonal conditions, recent dieting, or individual metabolic adaptation, even though those factors can affect real energy expenditure. BMR should also not be confused with TDEE.
Activity level is not an input to the BMR equation itself; it is applied afterward when estimating total daily needs. For tracking, use consistent body measurements and recalculate after meaningful changes in weight, age, or body size rather than treating one estimate as permanent.
Benefits of Using the BMR Calculator
- Establish a resting-energy baseline before activity factors are added to create a TDEE or maintenance-calorie estimate.
- Apply the Mifflin-St Jeor equations consistently without manually handling four inputs and the sex-specific constant each time.
- Separate resting energy needs from exercise calories, which prevents BMR from being mistaken for a complete daily intake recommendation.
- Recalculate after a meaningful body-weight change to keep a calorie-planning baseline aligned with current measurements.
- Use one standardized estimate when comparing nutrition scenarios instead of switching between unrelated rules of thumb.
Frequently asked questions
Is BMR the number of calories I should eat every day?
Not by itself. BMR estimates resting energy use. Daily maintenance needs are usually higher because normal movement, work, exercise, and digestion add energy expenditure beyond the basal level.
Which formula does this BMR Calculator use?
The script uses the Mifflin-St Jeor equations with weight in kilograms, height in centimeters, age in years, and a sex-specific constant.
Why does age reduce the BMR estimate?
Age appears as a negative term in the Mifflin-St Jeor equation. It represents the population-level tendency for resting energy expenditure to decline with age, not a direct measurement of an individual metabolic change.
Can two people with the same BMR need different daily calories?
Yes. Their activity, exercise, job demands, and other real-world factors can differ substantially. BMR is only the resting baseline used before those differences are considered.
Is this a direct metabolic test?
No. It is a mathematical estimate from body measurements and age. A laboratory measurement of resting metabolic rate uses physiological testing rather than an equation alone.
Final Words
Use the BMR Calculator to establish a resting-energy baseline before activity factors are added to create a TDEE or maintenance-calorie estimate. Keep in mind that weight and height raise the calculated BMR because larger bodies generally require more energy at rest under the equation.
For a second check, apply the Mifflin-St Jeor equations consistently without manually handling four inputs and the sex-specific constant each time. If the assumptions move, return to the BMR Calculator and test the new scenario before treating the earlier output as current.
Disclaimer
This calculator provides estimates for general informational and educational purposes only and should not be treated as financial, medical, legal, or professional advice. Results depend entirely on the accuracy of the figures you enter.
Always verify important decisions with a qualified professional, official documentation, or your financial institution before acting on any result shown here.
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