What is BMR and why do you need to know about it?

That’s the simple explanation. But understanding your BMR can be useful in weight management, whether you’re trying to lose, gain or maintain weight. 

We’ll explain the ins and outs of BMR, and let you know how you can calculate your own basal metabolic rate. We’ll also identify some of the factors that can influence your BMR. 

As we’ve said, your BMR is the amount of energy your body needs to perform the basal – or essential – functions that keep you alive. Usually, this is expressed in terms of the number of calories your body burns to do this.  

Sophie Thompson, specialist dietitian at the Princess Grace hospital, part of HCA Healthcare UK, tells us: “BMR is really difficult to measure. But roughly, BMR is normally 60 to 70% of your total energy expenditure”. We’ll explain more about how this is calculated below. 

Sometimes BMR is used interchangeably with RMR, or resting metabolic rate. But the two are slightly different. BMR is based on the absolute minimum of movement and only covers the essential functions of your body.  

RMR meanwhile, factors in some other basic functions, such as eating and going to the toilet. Generally, however, the two numbers will be similar for most people, with BMR being slightly lower than RMR. 

Knowing your BMR can be helpful in improving your health. If you know how much energy your body needs daily, this can help you to tailor your exercise and diet to achieve your goals.  

For example, if you want to lose weight (and check out our article on body composition to understand why it’s fat specifically, rather than weight, that you probably want to lose), you need to consume fewer calories than your body uses each day.  

Knowing your BMR can make it easier to calculate how many calories you can eat and still have a calorie deficit. Alternatively, it can help you work out if you need to start being more physically active. 

The same principle applies if you want to gain or maintain weight. Your BMR is a tool that can help you identify how many calories you need to consume to meet those goals.  

Thompson says, “It’s good to know what your BMI is to compare it to what calories you’re eating, and see that difference. 
 
And if it’s very vastly different and you want to lose weight, you might cut it down, or if you want to gain weight, you should be adding some calories on.”  

Your BMR is influenced by a range of factors, including: 

• Age – as we age, loss of muscle can reduce our BMR 
• Height – taller people tend to have a higher BMR than someone shorter 
• Gender – men typically have a slightly higher BMR than women 
• Body composition – higher muscle mass will generally equate to a higher BMR 
• Your activity levels 

• Your genetics 

Thompson adds, “The main thing that increases or decreases (but mainly increases) BMR is being acutely unwell. An infection can increase your BMR by up to 100% [compared to individuals of the same height, weight and gender]. 

Around five to ten percent variation can be due to body composition and how big someone’s organs are, variations in thyroid function, and cardiac rhythms.”

The good news is that you can make lifestyle changes that will also increase your BMR. More exercise, including weight training and high-intensity interval training, have been linked to increases in your metabolism.  

Muscle is what is described as ‘metabolically active tissue’, which means that, in principle, the more muscle you have, the more calories you will burn each day.  

The single most accurate method of assessing your BMR is by using a calorimeter in a controlled laboratory environment. This is not feasible for most people, but if you’re interested in getting an idea of your BMR, it can be done by using one of the many online calculators that are available.  

If you prefer to do the maths for yourself, then the most common way to do this is by using something called the Harris Benedict equation. The formula can be calculated as follows: 

• BMR for men = 66 + (13.7 × weight in kg) + (5 × height in cm) – (6.8 × age in years) 
• BMR for women = BMR = 655 + (9.6 × weight in kg) + (1.8 × height in cm) – (4.7 × age in years) 

Once you’ve worked out your BMR, the next step is to calculate your overall daily energy expenditure. This will give you an estimate of how many calories you need to consume each day to maintain your current weight. Multiply your BMR by a number that is linked to your daily activity level, as follows: 

• If you do little or no exercise: BMR x 1.2 
• Light exercise (1-3 days a week): BMR x 1.375 
• Moderate exercise (3-5 days a week): BMR x 1.55 
• Very active (6-7 days a week): BMR x 1.725 
• Extra active (for example, very hard exercise, and a physical job): BMR x 1.9 

This, or any other formula come to that, will not give you a perfect answer. But it will give you a ballpark figure to work with. Once you’ve worked out your overall calorie needs you can adjust your food intake and exercise levels to support the health goals you’ve set for yourself. 

BMR is calculated based on age, gender, height and weight. As a result, two individuals of the same sex, same height, same weight, and same age will, according to the equation, have the same basal metabolic rate.

“It’s really individual” says Thompson. This means that there is no such thing as a ‘normal’ or ‘good’ BMR, because it will vary based on those factors.

In general, someone shorter and lighter will have a lower BMR, and therefore a lower daily calorie requirement than someone taller and heavier. And if you lose or gain weight, that will also have a slight bearing on your BMR calculation.

But it’s important to remember that other factors such as body composition and genetics can influence your precise BMR. And to repeat what we said earlier, the equation will give you a ballpark figure for an average individual of your height and weight, rather than a number specific to you.

Understanding your BMR can be a useful tool to help you understand your energy requirements. In turn, you can then use this information to inform any lifestyle changes you want to make. It can, for example, help you to create a small, sustainable calorie deficit. Or it can help you ensure you aren’t consuming more calories than you need and stop you from gaining weight. 

If you’re looking for ways to boost your BMR, check out our guides to the benefits of strength training, HIIT workouts, or Reformer Pilates.