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Can You Really Trust A Calorie Calculator?

By Phil Graham

Renowned competitive body builder and Sports Nutritionist Phil Graham (BSc, CSSN) has established himself as one of UK’s leading fitness educators and coaches
Read more.

The relationship between the energy we consume and burn off matters a great deal when it comes to gaining or losing weight.

You measure the calories you eat by reading food labels or scanning them into fitness apps. You measure the amount of calories you burn off using pedometers, special watches and the ‘calories burned’ display on exercise machines.

You calculate individual calorie goals and build our diets within them, even if it includes the odd bit of junk food. As long as we’ve kept within the lines we’re good to go! Even major weight loss groups do the same with their unique point systems, which in reality are simply another way to track calories.

You could say the subject of calorie tracking is a pretty big thing nowadays. However, you need to ask yourselves are any of these measures really that accurate?

The purpose of this article is to investigate the validity and accuracy of calorie calculators. Are they the Holy Grail in our attempts to build muscle and lose fat? Or are they merely a rough guide?

Calorie Counting

What Is A Calorie?

man working out

In order to first understand why people use calorie calculators and counters it is important to gain a fundamental understanding ofwhat a calorie really is and why it’s important.

Essentially, calories represent the amount of energy that can be transferred between two bodies in the form of heat or mechanical work (activity).

I don’t want to go into great scientific depth on the laws of energy transfer and all the boring stuff on how a Cal is the amount of energy needed to raise 1 gram of water by 1 °C. or why Kcals are the typical measurement used when it comes to measuring food intake and energy expenditure through exercise.

Long story short - Calories provide energy.

You also need to understand the caloric value of the macro nutrients you consume from food.

  • Protein/Carbs – 4kcals/gram
  • Fat – 9kcals/gram

What Are Calorie Calculators?

food information

Calorie calculators aim to calculate our Basal Metabolic Rate, more commonly termed as your maintenance level of calories - the amount of energy you need to maintain energy balance.

Once BMR has been calculated, it is then correlated and multiplied against a self-perceived physical activity level to obtain a figure for ones Total Daily Energy Expenditure across the day.

This figure is then used to plan out an individual’s dietary intake specific to their unique goals of fat loss, muscle gain or body weight maintenance.

Common Misconceptions

A common misconception is following maintenance calories in the hope that it will maintain bodyweight. There is a big difference between weight gain, fat gain, fat loss and weight loss etc.

Both fat gain and fat loss are determined by energy balance. However, bodyweight can be influenced by a range of factors including fluid, sodium, carbohydrates and medication intake even when energy balance is in check.

Your maintenance level of calories is influenced by a number of factors. Each of these factors will vary greatly between individuals based on age, gender, genetic make up, levels of lean body mass, and metabolic adaptions to things like sickness, medication, under feeding, overfeeding, sleep deprivation and climate to name a few.

Basal Metabolic Rate (BMR)

This is the total energy requirement of the body at complete rest before eating, moving, or exercising (bed bound) at room temperature.


At rest energy the body requires fuel to run all its essential systems. These include everything form the central nervous system, right through to the workings of the reproductive system and everything else in between.

BMR is generally correlated with your lean body mass and to a lesser degree, your total body mass(1).

The larger the body mass, especially muscle, the higher the basal metabolic rate. Most moderately active individuals will burn in and around 60%-75% of their total energy intake from their basal metabolic rate(2).

Once you have established your BMR you then need to consider all the other variables that influence how energy is used and expended throughout the body. This includes everything from digestion of food to the voluntary act of opening the front door at the gym.

The thermic effect of food (TEF)

This relates to the energy burned of during the digestion and metabolism of food. It usually equates to around 10% of total calories consumed daily for individuals who eat a well balanced diet of carbohydrate, fats and protein (3).

If you eat 2500 kcals per day around 250kcal will be burnt of during via TEF.

Protein is considered the most costly nutrient to digest compared to carbohydrate and fat.

man running

Thermic effect of activity (TEA)

One of the biggest factors in determining your energy expenditure is your level of physical activity. The more you move, the more you burn – simple.

Both exercise and our day-to-day lifestyle are key influential factors.

When it comes to exercise you need to consider the type, duration and frequency of exercises. And, although relatively insignificant (4), the post exercise oxygen/energy consumption post exercise, which tends to be greater in higher intensity forms of exercise (crossfit) compared to lower (walking).

When it comes to career/lifestyle you need to consider job roles e.g. manual labor Vs. desk sitting, dog walking Vs. non dog walking etc.

A heavier individual who is highly active will burn of more energy than a lighter individual who has the same level of activity. You are moving the entirety of your bodyweight after all.

Non-Exercise Activity Thermogenesis (NEAT)


Non-Exercise Physical Activity (NEPA)

The amount of energy or calories burned through intentional movement such as carrying the shopping or helping move furniture.

How Many Calories Do I Need A Day Then?

woman measuring her waist

Once you have established your maintenance levels of calories you can adjust your food intake toward fat loss and or muscle gain, whichever your preference.

  • For fat loss you need to burn off more energy than you take in.
  • For mass gain you need to eat more energy than you burn off.

Slow tactful adjustments in energy balance (up or down) work better than extreme fluctuations at safe guarding muscle mass, avoiding unwanted fat gain and promoting better diet adherence.

Popular Calorie Equations – An Overview

There are a wide range of formulas used to calculate basal metabolic rate.

Researchers developed these formulas by analyzing indirect respirometry data from test populations of different ages, genders and body compositions. In layman’s terms respirometry calculates metabolic rate by measuring the ratio of gases expired by the body under set conditions.

Typical Calculation Process

  • Calculate BMR using Equation
  • Work out Total Daily Energy Needs by correlating BMR value with a perceived physical activity level/factor.
Woman Using Kettlebells

There are a wide number of formulas to use but investigating each of them is well beyond the scope of this short article. Let’s look at 3 of the most popular equations that are used in the fitness world; this includes the ones used in popular apps and online web calculators.

Please note: I have not reviewed calculations that account for %body fat or lean mass as this data usually isn’t to hand with the majority of the population looking a quick reference value…

Test Subject

30-year-old male weighing 100kg (220lbs) and 173cm tall

Stage 1 – Calculating Basal Metabolic Rate

1. Miffin –St Jeor Equation

  • Men: (10 x weight in kg) + (6.25 x height in cm) – (4.92 x age) + 5
  • Women: (10 x weight in kg) + (6.25 x height in cm) – (4.92 x age) – 161

2. The Revised Harris Benedict Equation

  • Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
  • Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)

3. The Owen Equation

  • Men: 879 + (10.2 x weight in kg)
  • Women:: 795 + (7.2 x weight in kg)

Once BMR has been calculated you then need to work out how many calories are roughly burnt of through exercise and daily movement. This is worked out by multiplying by a self perceived physical activity factor, see below:

  • Sedentary (Little or No Exercise, Desk job) - BMR x 1.2
  • Lightly Active (Light exercise/Train 3-5 days per week) - BMR x 1.3-1.4
  • Moderately Active (Moderate Exercise - Train 3-5 days per week) - BMR x 1.5-1.6
  • Very Active (Active lifestyle/Hard training 6-7 days per week) - BMR x 1.7-1.8
  • Extremely Active (Extremely active/Fitness/Manual job/ x2 Pday training) - BMR x 1.9-2.0

These physical activity factors do not take into account the Thermic Effect of Feeding, although small it still leaves scope for inaccuracy in the final total.

How The Calculations Compare For BMR

  • Miffin –St Jeor Equation = 1938.4kcal
  • The Revised Harris Benedict Equation = 2087kcal
  • The Owen Formula = 1899kcal

As you can see, the end calculations for BMR were different for each equation. And, this is even before you account for the individual’s physical activity.

Physical Activity Pyramid

The most extreme difference was between The Harris Benedict Equation and The Owen Equation, which gives a difference of 188kcal per day. Over the course of 7 days this equates to 1316 kcals.

Regardless it’s clear to see that the main underlying value of BMR differs between calculations and will thus cause further inaccuracies down the line when multiplied by the self-perceived physical activity level.

It’s also worth noting that these inaccuracies could be worsened by inaccurate body composition measures. Which are known to have large scope for error especially when calculated using the most popular assessments specifically skin folds, Bioelectrical impedance and Bod Pods.

Implications For Use

The obvious implication for this would be sub optimal fat loss, muscle building progress and performance.

Also bear in mind these equations don’t account for:

  • The adaptive component of metabolism (Starvation, Overfeeding, Sickness, climate change, NEAT – Anxiety etc.)
  • Body composition – those with higher levels of muscle mass will burn more than their fatter counterparts.
  • Medication use and its ability to speed/slow metabolic rate

It is therefore possible to run the risk of overeating and gaining unwanted body fat if one’s metabolism isn’t up to power. Or, on the flip side under eating, which would increase the potential for decreased performance, elevated hunger, increased potential to cheat on ones diet and increased loss of valuable muscle tissue.

How Do You Know You’re Eating Too Much or Too Little?

food diary

During the course of any muscle gain or fat loss diet it’s important to track changes in composition and performance.

The subject of assessing body composition is vast and beyond the scope of this article. However, the result achieved from any technique just like that from the calorie calculator mustn’t be taken with 100% trust. The fact so many methods exists highlights the obvious fact there are degrees of error with each method.

A simpler way would be to keep a food diary, track your average daily calorie intake, average body weight change over time and keep a close eye on the mirror. You’ll soon identify unwanted fat gain or muscle loss and thus be able to tweak nutrition up or down from there.

Other Things To Consider

nutritional information

You also need to bear in mind that food labels are not entirely accurate either and merely average calorific values of the food measured at a specific time. Factors such as climate, time of year, species of plant, and animal’s access to food are all important factors that dictate the end nutrient and energy composition of a food.

Even still tracking food intake with a set of digital scales can prove useful as it gives us a ball park level of energy to work with and measure changes against. Again, not perfect but it’s better than not having any idea at all.

  • Trying to be absolutely perfect with your calorie tracking will drive you mad.
  • Not one formula will give you an exact measure of how many calories you burn off on a daily basis (6).
  • Calorie calculators are an estimate not a measure and should never be relied upon with 100% certainty.
  • Regardless, no matter how inaccurate they still provide a starting point to work from. It’s simply a matter of tracking changes in body composition over time and observing how things change. As such, individuals must be pro active in tweaking their energy intake and expenditure up and down as required, to chase their goal.
Phil Graham

About Phil

Renowned competitive body builder and Sports Nutritionist Phil Graham (BSc, CSSN) has established himself as one of UK’s leading fitness educators and coaches.  He has helped coach and inspire a diverse range of clientele ranging from personal trainers, everyday members of the public right through to professional athletes across a wide variety of sports.

Phil educates 1000's of personal trainers each year through his seminars, workshops and attendance at some of the world’s largest health and fitness exhibitions. He actively writes for almost every major fitness publication, hosts the ever popular Podcast Elite Muscle Radio Podcast (available on iTunes) and works as Genetic Supplements resident nutrition expert for product development. He is also in the process of writing his first book, The Diabetic Muscle and Fitness Guide.

Phil’s coaching and personal training is based in Belfast Northern Ireland, he also offers online consultancy for those that cannot reach him locally.

You can connect with Phil on Facebook, Twitter, YouTube and Instagram.

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