Basal Metabolic Rate (BMR) Calculator

What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR), also referred to as basal energy expenditure, is the minimum amount of energy (measured in calories) your body needs to sustain vital, involuntary functions at absolute rest: breathing, blood circulation, hormone synthesis, cellular repair, and body temperature regulation.

Basal calories account for approximately 60% to 75% of your total daily energy expenditure in sedentary to moderately active individuals. The remaining calories burned each day are split between physical activity and exercise (~15% to 30%) and the thermic effect of food (TEF, ~10%), which is the energy required to digest and absorb nutrients.

At complete rest, internal organs account for the bulk of energy consumption: the liver expends around 27%, the brain 19%, the kidneys 10%, and the heart 7%. Understanding how many calories your body burns at rest is the foundational step in determining how many calories you should eat per day, whether your goal is maintaining weight, losing fat, or building muscle.

Formulas to Calculate Basal Metabolic Rate (BMR) and Daily Calories

Several predictive equations exist to estimate daily calorie expenditure based on weight, height, age, and sex. The Mifflin-St Jeor equation (1990) is widely considered the clinical gold standard, endorsed by the Academy of Nutrition and Dietetics for its superior accuracy in modern populations. Compared to the older Harris-Benedict equation (1919), Mifflin-St Jeor provides more reliable estimates and tends not to overestimate basal calorie needs.

Mifflin-St Jeor Equation for Men (kcal/day):

Mifflin-St Jeor Equation for Women (kcal/day):

The difference between the two equations lies in the final constant: +5 for men versus -161 for women. This adjustment accounts for typical physiological differences in body composition, as higher average lean muscle mass increases basal metabolic expenditure.

Once your BMR is determined, it is multiplied by your physical activity factor to calculate your Total Daily Energy Expenditure (TDEE), which represents your maintenance calories (the exact calorie intake required to maintain your current weight):

Step-by-Step Example: How to Calculate Daily and Maintenance Calories

Consider a practical calculation for a 30-year-old man who is 175 cm tall and weighs 75 kg, with light physical activity (exercise 1 to 3 times per week):

1. Step 1 - Apply the basal formula: BMR = (10 × 75) + (6.25 × 175) - (5 × 30) + 5
2. Step 2 - Calculate basal calories: BMR = 750 + 1093.75 - 150 + 5 = 1699 kcal/day at rest.
3. Step 3 - Calculate maintenance calories (TDEE): 1699 × 1.375 (light factor) = 2336 kcal/day to maintain current body weight.

Now consider a 25-year-old woman who is 165 cm tall and weighs 60 kg, with moderate physical activity (exercise 3 to 5 times per week):

1. Step 1 - Apply the basal formula: BMR = (10 × 60) + (6.25 × 165) - (5 × 25) - 161
2. Step 2 - Calculate basal calories: BMR = 600 + 1031.25 - 125 - 161 = 1345 kcal/day at rest.
3. Step 3 - Calculate maintenance calories (TDEE): 1345 × 1.55 (moderate factor) = 2085 kcal/day to maintain current body weight.

How Many Calories Should You Eat Per Day to Lose Weight?

To lose body weight sustainably, you must establish a caloric deficit: consuming fewer calories than your total daily expenditure (your TDEE or maintenance calories). Under a controlled deficit, the body draws on stored adipose tissue for fuel. Approximately 1 kg of body fat contains 7700 calories (or about 3500 calories per pound).

Our calculator estimates target daily calorie intake based on your monthly weight loss goal: losing 1 kg per month requires a deficit of approximately 253 kcal per day (7700 ÷ 30.4 days); losing 2 kg per month requires a deficit of 506 kcal per day. For example, if your maintenance expenditure is 2336 kcal/day, consuming around 2083 kcal or 1830 kcal per day allows steady, progressive weight loss.

A moderate deficit of 300 to 500 kcal per day is widely recommended as safe and sustainable while protecting lean muscle mass. You should generally avoid eating below your Basal Metabolic Rate (BMR) without medical supervision, as doing so can deprive your body of essential energy needed for basic cellular and metabolic processes.

Difference Between Basal Metabolic Rate (BMR) and Maintenance Calories (TDEE)

A frequent point of confusion when planning nutrition is mistaking basal metabolic rate for the total calories you should consume each day. These two metrics serve distinct physiological purposes:

• Basal Metabolic Rate (BMR): The baseline calorie burn required solely for vital organ function at rest (breathing, cardiac output, brain activity). It is the metabolic floor below which you should not restrict intake long term.
• Maintenance Calories (TDEE): Your actual total daily energy expenditure, combining BMR with occupational movement, daily activities, and planned workouts. Consuming this exact number keeps your weight stable.

In clinical settings, professionals also measure Resting Metabolic Rate (RMR), which is similar to BMR but measured under less restrictive conditions (such as including mild digestive activity). For practical everyday dieting and fitness goals, calculating BMR via Mifflin-St Jeor and applying your activity multiplier is the most accurate and accessible approach.

References

1. Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2), 241-247.
2. Frankenfield, D., Roth-Yousey, L., & Compher, C. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. Journal of the American Dietetic Association, 105(5), 775-789.
3. Harris, J. A., & Benedict, F. G. (1918). A Biometric Study of Human Basal Metabolism. Proceedings of the National Academy of Sciences, 4(12), 370-373.