BMR, Basal Metabolic Rate indicates how many calories a day an individual’s body needs for performing basic metabolic functions such as keeping vital organs functioning. BMR is calculated when you are awake, and your digestive system is inactive. This requires a 12-hour fasting period before an accurate BMR calculation.
Use the below BMR calculator to calculate yours. Learn more about how to use BMR for weight loss and other things related to BMR below.
The following equations are all validated ways of calculating BMR. The Mifflin-St Jeor Equation is the most commonly used one for BMR calculators (and the one that the BMR calculator on this page uses).
A = age
F = body fat percentage (only used in Katch-McArdle Formula)
H = body height in centimeters
W= body weight in kilograms
All the variables above influence BMR calculation. The only variables in the equations that one can change are body weight and body fat percentage. Muscle mass influences BMR, although it is not necessarily captured in the equations.
For example, comparing two people who have the same height, age, weight, and gender but one person who has more muscle mass. The two people will have the same BMR calculation. However, we know that the person with more muscle mass will need to consume more calories to maintain homeostasis since more muscle requires more energy. This is why the Katch-McArdle Formula includes body fat percentage but does away with gender (since the body fat percentage variable is a more accurate indicator of muscle mass than gender).
From the BMR calculator, you can see that losing weight also decreases your BMR. This means that the more weight you lose, the less energy (calories) your body needs to maintain homeostasis. This has implications for weight loss strategies.
BMR calculators are a good starting point to plan your weight loss strategy. By calculating the minimum amount of calories needed to maintain weight, you know that consuming more than that amount will lead to weight gain.
BMR calculators fall short by taking into account physical activity levels since the measurement is taken at rest and after a fast. Even basic activities increase how much energy your body needs to maintain homeostasis.
Good to know:
Use the Total Daily Energy Expenditure calculator (TDEE) to take your activity level into account.
As you lose weight, your BMR goes down. This means that if you want to continue to lose weight, you need to eat even fewer calories. Here’s an example:
A female aged 35 who weighs 75 kg and is 169 cm tall has a BMR of 1515 calories per day. If this person loses 10 kilos, their BMR drops to 1419 calories per day. That means that if this same person wants to keep losing weight, they need to continually lower their daily caloric intake to maintain the same rate of weight loss.
Suppose they always eat the same amount of calories no matter their weight. In that case, eventually, their weight loss will plateau (unless the daily caloric intake is absurdly low, to begin with, which is not advised for sustainable weight loss).
Resting Metabolic Rate (RMR) and BMR are often used interchangeably despite there being a fundamental difference. RMR is not calculated when one’s body has reached total equilibrium. Therefore, RMR is easier to measure since you do not have to achieve a fully inactive state.
BMR calculators are a great starting point for figuring out your weight loss or gain journey. However, individuals vary; therefore, BMR is an accurate calculation on a population level but could be inaccurate on an individual level. Additionally, research has noted variations in the accuracy of BMR calculations compared to non-Western/European populations. Recent research on BMR from the University of Cambridge has also found that BMR tends to be overestimated in certain populations. Research from The American Journal of Clinical Nutrition on BMR also found that gender and age have little effect on BMR, while lean body mass is a better indicator of BMR.
As stated, BMR calculators are a great starting point. The most effective way to design a weight loss strategy that is healthy, sustainable and achieves results will be worked out with a qualified medical professional.