The Legion BMR Calculator accurately estimates your basal metabolic rate (BMR)—the amount of energy your body requires to maintain essential bodily functions while at rest in a temperate environment, having not eaten for several hours. 

You can use the results from our BMR calculator to lose weight, gain muscle mass, or maintain your physique. 

Calories based on activity level

No activity (sedentary) 2,053
A little activity(1 to 3 hours of exercise or sports per week) 2,321
Some activity(4 to 6 hours of exercise or sports per week) 2,679
A lot of activity(7 to 9 hours of exercise or sports per week) 3,036
A TON of activity(10+ hours of exercise or sports per week) 3,393


What Is BMR?

Your basal metabolic rate, or BMR, is a hypothetical estimate of the amount of energy your body burns to maintain essential bodily functions like breathing, pumping blood, producing hormones, and so forth. In other words, it’s the number of calories you’d burn while resting for 24 hours.

Your BMR is a hypothetical estimate because it changes based on various factors, including your diet, environmental conditions, and stress levels. As such, it’s impossible to pinpoint exactly what your BMR is at any one time.

Consequently, scientists rely on mathematical models to predict your BMR since they can’t measure it directly.

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What Is a BMR Calculator?

A BMR calculator applies specific formulas to estimate an individual’s BMR, taking into account personal attributes such as age, gender, height, and weight. 

BMR calculators are especially useful when designing diet plans, as they provide insights into the minimum caloric intake necessary for basic physiological functions.

BMR calculations are based on standardized equations, which, while not able to calculate BMR perfectly, offer a useful baseline for understanding your caloric needs.

How to Calculate BMR without a BMR Calculator

The easiest way to calculate your BMR is to use the basal metabolic rate calculator (or “BMR calculator”) above.

You can also crunch the numbers yourself if you prefer.

There are several equations for this, but I suggest the Mifflin-St Jeor equation:

For men: BMR = 10 x weight (in kg) + 6.25 x height (in cm) – 5 x age (in years) + 5

For women: BMR = 10 x weight (in kg) + 6.25 x height (in cm) – 5 age (in years) – 161

I favor the Mifflin-St Jeor equation over other formulas, like the Katch-McArdle or Harris-Benedict equation, as it generates accurate results without requiring much math or your body fat percentage.

How to Use A BMR Calculator to Lose Weight

Once you’ve used a BMR calculator to determine your BMR, you can calculate your total daily energy expenditure (TDEE), which is the amount of energy (calories) you burn daily based on your body weight, height, age, and activity level.

You can then use your TDEE to calculate a daily calorie goal that puts you in a “calorie deficit” and drives weight loss

To do this, most experts recommend multiplying your BMR by the multiplier below that best describes your activity level:

  • Sedentary: 1.2
  • Lightly Active: 1.375
  • Moderately Active: 1.550
  • Very Active: 1.725
  • Extra Active: 1.9

These multipliers have undoubtedly helped many people lose fat, gain lean body mass (muscle mass), and maintain their physique. However, based on my experience assisting tens of thousands of people, these multipliers often overstate your energy expenditure.

In other words, if you use the above multipliers, you’ll probably place yourself in too small of a calorie deficit when cutting and too large of a surplus when bulking, thwarting your efforts to optimize your body composition

Therefore, I recommend using lower activity multipliers.

Here’s my approach:

Legion Activity Multipliers

Resting Metabolic Rate (RMR)

When searching for information on BMR calculators, you’ll probably come across a similar but slightly different measurement known as your resting metabolic rate (RMR).

Unlike BMR, which estimates the calories your organs need daily to function, your RMR indicates the calories you’d burn if you spent a day reclining in a chair.

Since the numbers are almost exactly the same, you can use both numbers more or less interchangeably for weight loss purposes. Technically, however, your RMR is slightly higher than your BMR.

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What’s A “Normal” BMR?

There’s no such thing as a “normal” BMR since factors individual to you, such as sex, age, height, and weight, dictate your BMR.

A BMR calculator lets you gain insight into your unique baseline energy expenditure. However, this approach provides an estimate at best, as it’s based on average metabolic rates. 

While it can’t pinpoint your exact BMR, using a BMR calculator to calculate your BMR can give you a useful starting point for manipulating your body composition. That is, you can use the results from a BMR calculator to lose weight, gain muscle, or maintain your current physique. 

Factors that Affect BMR

  • Age: Beyond the age of 60, your BMR decreases, mainly because you lose muscle mass.
  • Muscle Mass: The amount of muscle mass you have plays a pivotal role in determining your BMR. Muscles are metabolically active, requiring more energy at rest than tissues like fat. As a result, those with more muscle mass usually have a higher BMR.
  • Diet: Eating fewer calories than your body burns (a “calorie deficit”) for an extended period slows your metabolic rate. This often happens because a calorie deficit can lead to muscle mass loss.
  • Supplements: Certain supplements can affect your BMR. For instance, caffeine can temporarily increase your BMR.
  • Pregnancy: BMR can increase by up to 30% throughout pregnancy.
  • Climate: Research suggests that BMR may be higher in the winter than in the summer due to the energy your body expends keeping you warm.
  • Menstrual Cycle: BMR increases in the luteal phase of the menstrual cycle, mainly due to a rise in progesterone levels.
  • Stress: Periods of high stress can increase BMR as the body releases more cortisol and catecholamines, which stimulate metabolism.

FAQ #1: What is the most accurate BMR calculator?

If you don’t know your body fat percentage, BMR calculators that use the Mifflin-St Jeor equation tend to produce the most accurate results.

If you know your body fat percentage, BMR calculators using the Katch-McArdle equation may be slightly more accurate.

BMR calculators using the Harris-Benedict equation are typically the least accurate.

FAQ #2: What is a good BMR for my age?

It’s difficult to say what a “good” BMR is based solely on age—gender, height, and weight are crucial elements in this equation.

When pondering “what is my BMR,” it’s important to understand that your body’s metabolic rate naturally shifts as you get older, decreasing by around 1% per year beyond the age of 60.

The best way to maintain a healthy BMR for your age is build muscle, and to learn how to do that, check out this article:

How to Build Muscle in Your 40s and Beyond

FAQ #3: How do you use a BMR Calculator to gain weight?

The best way to use a BMR calculator to gain weight is to use it to estimate your TDEE, which you can then use to create a meal plan for building muscle. 

If you’d prefer to skip the math, aim to eat 16-to-18 calories per pound of body weight per day. This is enough to gain muscle mass and strength while gaining very little body fat.

+ Scientific References