Basal Metabolic Rate (BMR) Calculator

What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR), also known as Basal Metabolism or Basal Energy Expenditure, is the minimum amount of energy (measured in calories) that your body needs to maintain its vital functions at absolute rest: breathing, blood circulation, temperature regulation, brain function, and hormone synthesis.

Your BMR represents between 60% and 75% of your total daily energy expenditure. The rest is divided between physical activity (~20%) and the thermic effect of food (~10%), i.e., the energy your body uses to digest food.

Interestingly, most of the energy you consume at rest is not spent on mechanical work (like contracting muscles), but on maintaining the balance of fluids and ions between the body's cells. The organs that consume the most energy at rest are the brain, liver, and central nervous system.

How to Calculate Basal Metabolic Rate with the Mifflin-St Jeor Equation

The Mifflin-St Jeor equation (1990) is considered the most accurate formula for estimating Basal Metabolic Rate in healthy adults, according to the American Dietetic Association. Unlike the Harris-Benedict equation (1919), it was developed with more recent and representative population data.

Formula for Men:

Formula for Women:

The difference between both formulas is the last term: +5 for men and -161 for women. This reflects that men tend to have greater muscle mass and therefore a higher basal metabolic rate.

Once you have obtained your BMR, you must multiply it by the corresponding physical activity factor to get your Total Daily Energy Expenditure (TDEE), as shown in the following image:

Step-by-step basal metabolic rate calculation example

Let's look at a practical example for a 30-year-old man who is 175 cm tall, weighs 75 kg, with light physical activity (1-3 times per week):

1. Step 1 - Apply the formula: BMR = (10 × 75) + (6.25 × 175) - (5 × 30) + 5
2. Step 2 - Solve: BMR = 750 + 1,093.75 - 150 + 5 = 1,698.75 kcal/day
3. Step 3 - Adjust for activity: TDEE = 1,698.75 × 1.375 (light factor) = 2,336 kcal/day

Now an example for a 25-year-old woman who is 165 cm tall, weighs 60 kg, with moderate activity (3-5 times per week):

1. Step 1 - Apply the formula: BMR = (10 × 60) + (6.25 × 165) - (5 × 25) - 161
2. Step 2 - Solve: BMR = 600 + 1,031.25 - 125 - 161 = 1,345.25 kcal/day
3. Step 3 - Adjust for activity: TDEE = 1,345.25 × 1.55 (moderate factor) = 2,085 kcal/day

How to Use Basal Metabolic Rate to Lose Weight?

If you consume fewer calories than your Total Daily Energy Expenditure (TDEE), you create a caloric deficit that forces your body to use stored fat as an energy source. 1 kg of body fat is equivalent to approximately 7,700 calories.

For example, if your TDEE is 2,000 kcal/day and you want to lose 1 kg of fat per month, you need a deficit of 7,700 ÷ 30 = 257 kcal per day. That means you should consume around 1,743 kcal per day.

A deficit of 500 to 750 kcal per day is considered safe and sustainable, allowing you to lose between 0.5 and 0.7 kg per week. More aggressive deficits can lead to muscle loss, fatigue, and adverse metabolic effects.

What is the Difference Between BMR and RMR?

Although they are often used as synonyms, Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) are not exactly the same:

• BMR: Measured under strict conditions of absolute rest: after 8 hours of sleep, 12 hours of fasting, in a thermally comfortable environment, and without prior physical or mental activity. It is the actual minimum energy expenditure.
• RMR: Measured under less restrictive resting conditions. It includes the energy used to digest food (postprandial thermogenesis), so it is typically 10% to 20% higher than BMR.

In clinical practice, RMR is used more frequently because it is easier to measure. For diet calculation purposes, the difference between the two is minimal.

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.