BMR Calculator (Basal Metabolic Rate, Mifflin St Jeor Equation)

Developed in 1990, the Mifflin St Jeor equation is widely recognized by clinical dietitians and researchers as the gold standard for estimating resting energy expenditure. The mathematical model accounts for your body weight in kilograms, height in centimeters, and age in years, with separate constants for men and women to reflect differences in average body composition.

For men, the formula is: BMR = (10 * weight) + (6.25 * height) - (5 * age) + 5. For women, the formula is: BMR = (10 * weight) + (6.25 * height) - (5 * age) - 161. Note that height must be converted to centimeters and weight to kilograms if you are entering imperial measurements. This baseline value can then be multiplied by a Physical Activity Level (PAL) factor to determine your Total Daily Energy Expenditure (TDEE).

Let us calculate the BMR for a 31-year-old female who is 168 cm tall and weighs 65 kg using the Mifflin St Jeor equation for women.

Step 1: Multiply weight in kilograms by 10. (65 * 10 = 650)

Step 2: Multiply height in centimeters by 6.25. (168 * 6.25 = 1050)

Step 3: Multiply age in years by 5. (31 * 5 = 155)

Step 4: Combine these values according to the formula: 650 + 1050 - 155 - 161.

Step 5: Perform the final arithmetic. 1700 - 155 = 1545. 1545 - 161 = 1384 calories per day.

Her baseline resting metabolic rate is approximately 1,384 calories per day.

Your BMR is only the baseline representing complete rest; do not eat at this exact calorie level unless advised by a medical professional, as your total daily burn is significantly higher once everyday movement and exercise are factored in. Keep in mind that equations are statistical estimates with a small margin of error, so track your weight and energy levels over two to three weeks to fine-tune your daily calorie targets. Lastly, remember that as you lose or gain weight, your BMR changes, meaning you should recalculate your numbers every few months to prevent weight-loss plateaus.