Calculating calories and macro's: A detailed guide.

Whatever your health and fitness goals, it is important that we provide the body not only with the correct amount of fuel to support the process but that we are getting it from the right nutritional sources. In order to do this we need to estimate how many calories we need to sustain our current energy levels, often referred to as maintenance calories, from which we can then create a platform to meet our future goals from an energy and nutrient requirement perspective. We can then adjust these accordingly with fat loss, muscle growth or performance in mind.

So how do we calculate a starting point?

There are many different formula and methods to calculate your overall energy requirements however a vast majority of these are going to be inaccurate for a wide variety of reasons, including individual variance in metabolism, how much lean tissue a person carries, how active they are or perceive they are and an inability to accurately recall food intake if using past dietary history to inform a starting point.

The key here is that no matter what method you use, that once you have calculated a starting point that the diet is adjusted accordingly depending on changes in appearance, performance etc. Obviously if the goal is weight loss and weight starts to creep up then calories need to be reduced each week until weight loss kicks in and vice versa if you are looking to build muscle (however growing muscle is a slow process so measures of performance and strength increases will be better gauges of progression than weight alone). View CSN's diet and fat loss range here.

Harris-Benedict Equation

The simplest version of a scientific approach to calculating energy needs is the Harris-Benedict Equation (revised by Mifflin et al., 1990):

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5

Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) – 161

Total Calorie Requirements = BMR x Activity factor


Activity Factors: 1.2 = Sedentary/little or no exercise, 1.375 = light activity/exercise 1-3 days per week, 1.55 = Moderate activity/exercise 3-5 days per week,

1.725 = very active/hard exercise 6-7 days per week, 1.9 = Extra active/very hard exercise every day of the week.


For example, a 100kg male who is 185cm tall and 35 years of age takes part in hard training 6 days per week, therefore their requirements are…

BMR = (10 x 100) + (6.25 x 185) - (5 x 35) + 5 = 1000 + 1156.25 - 175 + 5 = 1976.25kcal

Total Calorie Requirement = 1976 x 1.725 = 3409kcal per day

How to calculate your macronutrient split?

Secondly, we need to consider where we get our ‘energy’ from. This is our macronutrients or ‘macros’... protein, fats and carbohydrates. There are two different approaches to calculating the amounts of macronutrients in the diet, firstly and most simply by using a ratio of protein, carbs and fats. For example, if we choose a conventional approach to a balanced nutrient intake designed to meet basic health requirements, then we might use a 15-20% protein, 50-60% carbohydrate and 20-30% fat ratio. If we were looking to build muscle or lose fat then we might increase our protein to 30-40% to support muscle growth/preserve muscle tissue whilst dieting and reduce intake either from carbohydrate or fats. Increasing your protein? Take a look at CSN's protein range.


In this case if we calculated we needed 2500kcal to maintain weight then our starting point would be, assuming a 30/40/30 ratio:

(2500/100)x30= 750kcal from protein which would equate to 187.5g of protein (750/4kcal per gram of protein)

(2500/100)x40=1000kcal from carbs which calculates to 250g of carbs (1000/4kcal per gram of carbohydrate)

(2500/100)x30=750kcal from fat providing 83g of fat (750/9kcal per gram of fat).

Ratio method for macronutrients

This is the simplest way to calculate your macro’s, however some people like to work out amounts that are goal specific for each macronutrient, especially when it comes to protein intake this will vary massively dependent on a person’s goal. For example, for endurance sports 1.2-1.4g/kg of bodyweight, for strength 1.4-1.8g/kg, muscle building 1.8-2g/kg and fat loss even higher at up to 2.5g/kg is recommended. Fat intake needs to be also considered at a level that will provide enough essential fatty acids and this is often suggested to be around 1g per kg of bodyweight.

Alternative method for calculating your macros - Do it backwords.

The second method uses these amounts and then works backwards to calculate carbohydrate intake. If we imagine the same person used in the above example weighed 80kg and still had a maintenance intake of 2500kcal and the goal was fat loss our starting point would be to calculate protein intake at 2.5g/kg and fat at 1g/kg, giving us amounts of 200g of protein (80kgx2.5g/kg) and 80g of fat (80gx1g/kg). This would mean that our calorie intake for protein would be 800kcal (200g x 4kcal/g) and 720kcal for fat (80g x 9kcal/g) giving us a total energy intake of 1520kcal for these two nutrients.

We then simply take our total calories and subtract this amount to work out how many calories for carbs we have left… 2500-1520=980kcal… and then divide this amount by 4kcal/g to calculate our carb intake... 980kcal/4kcal/g=245g of carbohydrate.

Benefits of calculating macros backwards

This may have benefits over the first method for a very important reason. Even though using the second method, assuming fat loss was the goal, then at 80kg the calculated protein intake of 200g is still in the ‘ball park’ of the previous'ratio' example (187.5g). However if we then reduced calorie intake by 300kcal to 2200kcal that might be required to cause fat loss, then by using the first ‘ratio’ method the amount of protein would now drop to 165g of protein and this amount would obviously be reduced further if we needed to further reduce calorie intake further down the line… and the last thing we should be doing when reducing calories for fat loss is reducing protein intake!

This also works the other way when building muscle. We know that consuming more protein is unlikely to increase muscle growth past a certain amount (2g/kg of bodyweight), therefore if we need to increase our calories it is highly likely this needs to mostly come from carbohydrates and/or fats, not protein. Then as we become bigger (or smaller) protein intake regulates directly to changes in weight, not changes in calorie intake which as we have seen can be less than ideal.

There are many apps and websites that can help

In summary calculating your macro’s although it might seem like a lot of maths, is actually fairly straightforward to do if you follow the process step by step. Fortunately, if maths or patience isn’t your forte then there are plenty of easy to use online calculators, or apps, that you can check your own numbers with to make sure you’re heading in the right direction… or you could just use these instead, but they might not be as specific to your goal as you might want! 

As always Team CSN are here to help, call or email us today and we can give you professional, unbiased advice on all your nutrition and supplement needs.