Vitamins & Minerals

What Is BMR and How Do You Calculate It?

BMR stands for basal metabolic rate and is the average amount of calories your body requires to keep your organs alive every day.

That is, it’s an estimate of the absolute minimum number of calories your body requires to sustain basic functions like breathing, hormone production, cellular repair, and nothing more.

You can accurately estimate your BMR by entering your gender, weight, height, and age in a BMR equation, or by entering the same information in the Legion BMR Calculator, which does all of the math for you.

Once you know your BMR, you can use it to create a meal plan that will help you lose, gain, or maintain your weight. 

Keep reading to learn how!

What Is BMR?

Your basal metabolic rate (BMR) is a hypothetical estimate of the amount of energy your body burns to maintain essential physiological functions, but nothing more.

This includes processes like pumping blood, breathing, regenerating cells, and so on.

The reason your BMR is a hypothetical estimate is that it changes based on a variety of factors including your diet, environmental conditions, activity, stress, sleep levels, and others, so it’s impossible to pin down exactly what your BMR is at any one time.

Thus, scientists use mathematical models to predict what your BMR is, since they can’t measure it directly.

Here’s a good way to think of it:

Imagine it’s 2091, and in order to protect ourselves from COVID-91, we’ve decided to upload our consciousness to the cloud and live in a state of suspended animation in an artificial amnion, receiving nourishment and mental stimulation from our technocratic overlords (you know, like this).

Your BMR would be roughly how many calories it takes to keep you alive under those circumstances.

There are many formulas for estimating BMR, but which one you pick mostly comes down to personal preference and convenience (you’ll learn the best ones in a moment).

You may have also heard of a similar but slightly different measurement known as your resting metabolic rate (RMR). This is the actual number of calories your body burns at rest, which can be influenced by factors like prior activity or food intake.

In other words, your BMR is the hypothetical number of calories your organs require each day to stay alive, while your RMR is the actual number of calories you would burn per day lying completely still, without eating or working out beforehand.

Thus, your RMR will be slightly higher than your BMR, although the absolute differences are miniscule and you can use both numbers more or less interchangeably for weight loss purposes.

How Does Calculating Your BMR Help You Lose Weight?

Whether you gain or lose weight is dictated by energy balance—the relationship between the energy you feed your body and the energy it expends.

In other words, calories in versus calories out.

While many people think exercise is the most effective way to burn calories (and it does help quite a bit!), your BMR typically accounts for the majority of the calories you burn every day.

For example, I’m 36 years old, 6’1 and 195 pounds, and my BMR is about 1,900 calories per day. On days I work out, I typically lift weights for about 45-to-60 minutes and do about 30-to-40 minutes of cardio, burning an additional ~500-to-800 calories on these days (depending on the volume and intensity of the workouts).

In other words, my BMR burns two-to-four times more calories per day than my exercise routine, and it does so even on the days I don’t train, without me having to lift a finger. Thus, your BMR plays a key role in supporting weight loss.

BMR vs. TDEE

Burning calories is only one side of the energy balance coin. To lose, gain, or maintain your weight, you also need to control how many calories you consume.

Knowing your BMR assists with this, too.

Once you know your BMR, you can use a few other formulas to estimate how many total calories you burn every day, known as your total daily energy expenditure (TDEE).

This number includes your BMR and the calories you burn from exercise, non-exercise activity, and the thermic effect of food (how many calories you burn digesting your meals).

Basically, your BMR is one component of your TDEE, which is a far more useful number to know when it comes to controlling your body weight. 

Once you know your TDEE, you can make effective decisions about how to eat based on three premises:

  • If you consistently eat more than that number of calories every day, you’ll gain weight.
  • If you consistently eat less every day, you’ll lose weight.
  • If you consistently eat that much, you’ll maintain your weight.

Now, if you’re shaking your head, thinking I’m drinking decades-old Kool-Aid, let me ask you a few questions.

Why has every single controlled weight loss study conducted in the last 100 years . . . including countless meta-analyses and systematic reviews . . . concluded that meaningful weight loss requires energy expenditure to exceed energy intake?

Why have bodybuilders dating back just as far . . . from Sandow to Reeves and all the way up the line . . . been using this knowledge to systematically and routinely reduce and increase body fat levels?

And why do new brands of “calorie denying” come and go every year, failing to gain acceptance in the weight loss literature?

The reality is that a century of metabolic research has proven, beyond the shadow of a doubt, that energy balance, which operates according to the first law of thermodynamics, is the basic mechanism that regulates fat storage and reduction.

Once you accept this premise, the science of weight loss becomes brutally simple (though not necessarily easy, as with most things in life). 

What’s the Best BMR Formula

The most accurate way to calculate your BMR is to go to a lab and hook yourself up to a metabolic cart.

Of course, this is also expensive and impractical.

Fortunately, it’s also unnecessary, because there are mathematical equations that can predict the results of one of these machines with decent accuracy.

There are many BMR formulas to choose from, but which one you pick mostly comes down to personal preference and convenience.

Personally, I use and recommend the Mifflin-St Jeor variant, which looks like this:

BMR = [9.99 x weight (kg)] + [6.25 x height (cm)] – [4.92 x age (years)] +/- (s), where “s” is +5 for men and -161 for women.

Or, to make things simpler, we can separate it into male and female versions:

Male BMR = [9.99 x weight (kg)] + [6.25 x height (cm)] – [4.92 x age (years)] + 5

Female BMR = [9.99 x weight (kg)] + [6.25 x height (cm)] – [4.92 x age (years)] – 161

The reason I recommend the Mifflin-St Jeor over other BMR formulas such as the Harris-Benedict or Katch-McArdle is it produces very accurate results on par with these equations, but doesn’t require much math or your body fat percentage.

One catch with the Mifflin-St Jeor equation is it assumes you have a relatively normal body composition (normal musculature and 10-to-20% body fat for men and 20-to-30% for women).

Thus, the equation can underpredict the BMR of people with above-average levels of muscle mass (especially if they also have below-average levels of body fat as well), and overpredict the BMR of people in the opposite boat.

So, why not use a BMR equation that incorporates lean body mass then, such as the Katch-McArdle equation?

That’s what I used to do and recommend, but I stopped for two reasons:

  • Most people have a hard time accurately estimating their body fat percentage, and relatively small mistakes can wipe out any potential benefits of the equation. That is, if the equation is 5% more accurate, but your estimate of body fat percentage is off by 20% (relative), it’s a wash.
  • The Mifflin-St Jeor equation is simpler and produces estimates that are almost identical to the Katch-McArdle equation for most people.

The first point is self-explanatory: many people think they’re significantly leaner than they are, which translates into an overestimated BMR with the Katch-McArdle equation. The second point requires a bit more explanation, though.

Although muscle does burn more calories than body fat, the differences are unimportant in practice.

Research shows that a pound of muscle burns around 6 calories per day (not 50, as many fitness gurus claim), and fat burns around 2 calories per day. That’s a threefold relative difference, but a trivial absolute difference that has little impact on your BMR.

For example, I have about 40-to-50 pounds more muscle than most guys my height (6’1, 195 lb., ~10% body fat, and 36 years old), and the Mifflin-St Jeor equation pins my BMR at 1,872 calories per day.

The Katch-McArdle equation, which accounts for my additional muscle mass and low body fat percentage, estimates my BMR is 2,089 calories per day—about 200 calories more. In the scheme of things, this is too little to matter.

And what about the Harris-Benedict equation?

This is also a workable formula that produces results similar to the others, but most researchers consider the Mifflin-St Jeor to be slightly more accurate. There’s also the Revised Harris-Benedict equation, which is considered a smidge more accurate than the original (but again, not quite as accurate as the Mifflin-St Jeor equation).

Finally, I want to share one more equation with you, which is handy because of its simplicity: the Lyle McDonald resting metabolic rate (RMR) equation. Here it is:

Male RMR: 11 x body weight in pounds

Female RMR: 10 x body weight in pounds

Yep, that’s it, regardless of your body composition.

As you now know, RMR is slightly different from BMR, but for our purposes here, they’re basically interchangeable.

My general recommendation is to use the Mifflin-St Jeor equation if you have a calculator to do the heavy lifting for you (like the Legion BMR Calculator) or you want to be as precise as possible, and the Lyle McDonald equation if you want a quick and dirty solution that’s almost as accurate in practice.

The Right Way to Think About BMR Formulas

No BMR formula is 100% accurate for all people under all circumstances. Your lifestyle, genetics, diet, and daily habits make your actual BMR a small and moving target that formulas are unlikely to hit. Heck, even the fancy devices for measuring BMR aren’t 100% accurate.

Luckily, BMR formulas don’t need to be pinpoint accurate to serve their intended purpose—they just need to be good enough so you know where to start. Then, you can raise or lower your calories based on how your body actually responds to your diet.

For instance, if you’re cutting and a TDEE equation (which includes BMR calculation) says you should eat 2,500 calories per day to lose weight, and you aren’t losing weight, then you need to eat less, regardless of what the math says.

Similarly, if you’re lean bulking, and a formula says you should eat 3,000 calories per day to gain weight, but you aren’t gaining weight, then you need to eat more.

The bottom line is that all BMR formulas are estimates of your actual BMR, not precise measurements. Use them to establish a starting point for your calorie intake, and then adjust up or down based on how your body responds. 

This is an important point to drive home, as many people agonize over whether or not they’ve “perfectly” nailed their BMR. Don’t make this mistake. Pick a BMR formula that catches your fancy, enter your numbers, create a meal plan, and get to work. Then you can adjust up or down based on your rate of progress.

How to Use a BMR Calculator to Lose Weight

This process has just three simple steps:

  1. Estimate your BMR using the Legion BMR Calculator.
  2. Use your BMR to estimate your TDEE.
  3. Use your TDEE to create and follow a meal plan that helps you lose, gain, or maintain your weight.

Normally, you’d have to do all of this by hand, but luckily for you, I’ve created a calculator that does most of the math for you (it even calculates how your calories should break down in terms of protein, carbs, and fat, depending on your goal). Check it out here.

The reason I said the calculator does most of the math for you is because once you know how many calories and grams of protein, carbs, and fat you should eat per day to reach your goals, you still have to turn these numbers into a meal plan made up of foods you enjoy.

Read these articles to learn how:

The Definitive Guide to Effective Meal Planning

How to Make Meal Plans That Work For Any Diet

Meal Prep Made Easy: How to Make the Perfect Meal Prep

And finally, if you’d like some help with this process, check out Legion’s custom meal planning service, or our pre-made meal plan templates for men and women.

+ Scientific References

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