A Simple and Accurate BMR Calculator (and How to Use It)

Just looking for an accurate BMR calculator and nothing else? Here ya go:

Not sure what a BMR calculator is, why you need it, or how to use it to lose or gain weight? Read on!

Key Takeaways

  1. BMR stands for basal metabolic rate and is the average amount of calories your body requires to keep your organs alive every day.
  2. You can accurately estimate your BMR with your gender, weight, height, and age.
  3. 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!

“Calories don’t count.”

“A calorie isn’t a calorie.”

“Calorie counting doesn’t work.”

“What you eat is more important than how much.”

These are some of the most harmful diet lies told by trainers, fitness magazines, and self-styled “gurus” that keep you from getting the body you want.

If you fall for them, weight loss will always be an uphill battle.

Learn the truth, however, and you can lose weight with ease while also eating foods you enjoy.

A big promise, I know, but it’s not an exaggeration.

So, what’s the big “secret” to effective weight loss?

Managing your energy balance properly.

Practically speaking, this means . . .

  • If you want to lose weight, you need to eat less energy than you burn over time.
  • If you want to gain weight, you need to eat slightly more energy than you burn over time.
  • If you want to maintain your current weight, you need to eat more or less the same amount of energy you burn over time.

That’s a tough row to hoe without hard numbers, though.

How do you quantify how much energy you’re burning over time? And how much less or more should you eat?

That’s where a BMR calculator comes into play.

BMR stands for basal metabolic rate, and it’s a mathematical estimate of how many total calories your body burns every day just to keep your organs alive.

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

The best BMR calculators work by using your weight and gender to estimate your BMR.

With this number in hand, you can then use other mathematical formulas to estimate how many total calories you burn every day, known as your total daily energy expenditure (TDEE).

And once you know your TDEE, you can then create a meal plan that allows you to systematically lose, gain, or maintain your weight.

In this article, you’re going to learn exactly what your BMR is, how calculating your BMR makes weight loss easier, how to calculate your BMR, the best BMR equations, and more.

Let’s start at square one: what is your BMR?

What Is Your Basal Metabolic Rate?

basal metabolic rate

Your basal metabolic rate 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.

Why is it a hypothetical estimate?

Well, your BMR changes based on a variety of factors including your diet, environmental conditions, activity, stress, and 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 (more on this 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.

Summary: Your BMR is an estimate of the minimum number of calories your body requires to stay alive for 24 hours.

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How Does Calculating Your BMR Help You Lose Weight?

You already know the short answer, but let’s take a closer look at how knowing your BMR helps you lose weight.

The thing that dictates whether you gain or lose weight is energy balance—the relationship between the energy you feed your body and the energy it expends.

In other words, calories in versus calories out.

Read: What 33 Studies Say About the CICO Diet for Weight Loss

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 vast 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 duration 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.

Neat, no?

Of course, 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 digestion of food.

And 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 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.

That doesn’t mean you have to count calories to lose weight . . . but it does mean you have to understand the relationship between calorie intake and expenditure and weight gain and loss.

Summary: Knowing your basal metabolic rate (BMR) allows you to calculate your total daily energy expenditure (TDEE), which you can then use to create meal plans that will help you lose, gain, or maintain your weight, eating foods you enjoy.

What’s the Best Way to Calculate Your BMR?


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 formulas such as the Harris-Benedict or Katch-McArdle is it produces very accurate results on par with other 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).

Read: How to Calculate Your Body Fat Percentage Easily & Accurately (With a Calculator)

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:

  1. 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.
  2. 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.

None of these BMR equations are 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.

Luckily, BMR equations 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 example, it’s possible the Mifflin-St Jeor equation slightly underpredicts my energy needs, and the Katch-McArdle equation slightly overpredicts my needs. I’ll never know my true BMR with absolute certainty (even fancy devices for measuring it aren’t 100% accurate), so all that matters is that I consistently eat the same amount every day, and adjust my calorie intake as needed.

So, 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.

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.

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.

Summary: All BMR equations 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.

How to Use a BMR Calculator to Lose Weight

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).

Here it is:

None (little to no physical activity) A little (one to three hours of exercise or sports per week) A moderate amount (four to six hours of exercise or sports per week) A lot (seven to nine hours of exercise or sports per week) A TON (ten or more hours of exercise or sports per week) Custom Activity Multiplier
Lose fat ("cut") Build lean muscle ("lean bulk") Maintain the same weight ("maintain")

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.

The Bottom Line on BMR Calculators

The single biggest hidden barrier to weight loss for most people is the failure to understand energy balance.

That is, if you don’t understand and embrace the fact that your weight is ultimately dictated by the relationship between how many calories you burn and consume, weight loss will always be hit-or-miss.

Once you understand how energy balance works, though, and how to turn it to your advantage, you can control your body fat levels with the same precision as managing a checking account.

And this process starts with determining your BMR.

Your basal metabolic rate (BMR) is an estimate of the minimum number of calories your body requires to stay alive for 24 hours.

Knowing your BMR allows you to calculate your total daily energy expenditure (TDEE), which you can then use to create enjoyable, healthy meal plans will help you lose, gain, or maintain your weight.

You can find many different formulas for calculating your BMR, but the one I use and recommend is called the Mifflin-St Jeor equation, which is what I used to create the Legion BMR Calculator.

After calculating your BMR, TDEE, and target calorie intake (based on whether you want to lose, gain, or maintain your weight), you just have to determine how your calories should break down into protein, carbs, and fat, and turn these numbers into a meal plan.

And if you stick to your meal plan, your body will change the way you want it to.

What’s your take on BMR calculators? Have anything else to share? Let me know in the comments below!

The post A Simple and Accurate BMR Calculator (and How to Use It) appeared first on Legion Athletics.