Basal Metabolic Rate Calculator
Your basal metabolic rate (BMR) refers to how much energy your body burns each day (measured in calories or kilojoules) just to keep itself alive.
For example, your vital organs like your heart, lungs, and brain burn energy 24 hours a day without any conscientious effort.
Your BMR represents approximately 60 to 75% of the total energy you burn each day (called total daily energy expenditure or TDEE). The remaining 30 to 40% are accounted for by your physical activity (i.e., exercise ~15-30%) and the thermic effect of food (i.e., energy burnt to digest food ~10%).
Is basal metabolic rate the same as resting metabolic rate?
You will often hear basal metabolic rate and resting metabolic rate (RMR) used interchangeably. But are they the same thing? Almost.
Your basal metabolic rate is generally measured in a relaxed, reclined position, after at least eight hours of sleep, and 12 hours of fasting so that your digestive system isn't ticking over and burning extra calories (i.e., the thermic effect of food).
Resting metabolic rate, on the other hand, can be measured under less restrictive conditions and could possibly be slightly higher depending on how active you were or what/when you ate before commencing the test.
What's the difference between estimated vs measured basal metabolic rate?
It is important to understand that there may be a difference between your ESTIMATED versus your actual MEASURED basal metabolic rate.
Indirect calorimetry is a laboratory test which, if performed correctly, can give you a more accurate picture of your measured metabolic rate. However, it is usually done in a clinical setting so may be unavailable, inconvenient, and/or cost-prohibitive.
Over my career, I have conducted countless indirect calorimetry tests and compared them with the estimates. In most cases, the numbers generally tend to align reasonably well, give or take 100 to 200 calories.
Also note that your basal metabolic rate is not necessarily the number of calories you're trying to eat each day. You'll still need to add additional calories to account for your daily physical activity levels.
If you're working with a trained health professional such as a dietitian, you may need to adjust the estimated numbers up or down a bit depending on your specific goals.
Mifflin St Jeor formula
This calculator uses the Mifflin St Jeor formula which is suitable for estimating resting energy expenditure in healthy people. The formulas are as follows:
Reference
Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO (1990). "A new predictive equation for resting energy expenditure in healthy individuals". The American Journal of Clinical Nutrition. 51 (2): 241–247. doi:10.1093/ajcn/51.2.241
