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How to Calculate your Macros - A Step By Step Guide

Step 1 - Calculate your BMR

The first step is working out your BMR by using the Katch-Mcardle formula:

BMR = 370 + (21.6 x Lean Body Mass(kg))

Lean Body Mass = (Weight(kg) x (100-(Body Fat %)))/100

To help calculate your body fat percentage use the US Navy calculator:

At Box Nutrition, we offer metabolic testing, the gold standard for calculating your BMR (metabolism).

Step 2 - Calculate your daily energy expenditure

Calculate your daily energy expenditure by estimating your Physical Activity Level (PAL).

This is a rough measure of your lifestyle activity and does not include planned or structured exercise but only day-to-day life.

Unless you have an active job, set your PAL at sedentary (we will later calculate activity from exercise).


  • Mostly inactive or sedentary: 1.2

  • Fairly active: 1.3

  • Moderately active: 1.4

  • Active: 1.5

  • Very active: 1.7

Step 3 - Estimate energy expenditure through exercise

Estimate the number of kcals you will expend during exercise using the MET scale or with the use a fitness wearable.

Each day of the week can be defined by the amount of activity performed. A recovery day or day without a workout would be classed as a “light day”. Training once would be classified as a “moderate day”, and days where you train twice would be classed as “hard days”.

VO2Max testing or metabolic testing is another way to accurately measure your kcal and carbohydrate:fat burn during exercise.

What about the Thermic Effect of Feeding (TEF)?

Although TEF can account for an additional 5-10% of your total energy expenditure (TEE), this is only a rough estimate, as the amount and type of food you eat will alter this number. Protein has a far higher TEF than carbohydrates and fat. Roughly 25% of the kcals from protein eaten will be lost as heat, whereas only around 70–75% will be absorbed. Carbohydrates may lose 10% as heat, whereas fat may only lose 2-3%. As this figure will vary day-to-day and only has a small bearing on your TEE, we therefore recommend not to worry too much about the impact of TEF.

If you struggle to put on weight or you want to be as accurate as possible with your starting estimates, then you may want to account for TEF by adding 5-10% to your TEE.

Step 4: Adjust for body composition goals

Add the figures from steps 2 and 3. This is the number of kcals you need to maintain your body weight.

  • If your goal is to lose weight, reduce your kcal intake by 15%. This is done by multiplying your figure by 0.85.

  • If your goal is to gain weight, increase your kcal intake by 20%. This is done by multiplying your figure by 1.2

If you wanted more help with improving performance and fat loss, check out our nutrition coaching here.

Calculate your macros

Step 5: Calculate your protein

To calculate your daily protein intake:

Multiply your lean body mass by 2.3-2.5 or 1.6-2.0 of your TARGET bodyweight

The number you calculate is the recommended number of grams of protein you are advised to eat in a day.

Step 6: Calculate your fat

A good starting point for your fat intake is between per day. If you prefer more fat in the diet, then go for the higher number. If you perform higher intensity, prolonged moderate/high intensity (<70%MHR) or high-volume resistance training then aim for the lower range.

If your primary activity is a low volume sport such as powerlifting or Olympic weightlifting, or your goal is weight loss, then you may choose to increase your fat intake above this recommendation. This will mean that a smaller proportion of your food will come from carbohydrates.

Step 7: Calculate your carbohydrates

Carbohydrate intake is calculated by the kcals left over after working out your fat and protein needs. To do this, use the following conversions:

  • Fat kcals = fat in grams × 9 (There are 9 kcals per g of fat)

  • Protein kcals = protein in grams × 4 (There are 4 kcals per g of protein)

  • Carbohydrate kcals = total daily kcals – fat kcals – protein kcals

  • Carbohydrates in grams = carb kcals ÷ 4 (There are 4 kcals per g of carbohydrates)

Endurance athletes

If you're an endurance athlete, my advice is to swap steps 6 and 7 around as it is more important to get match your carbohydrates with the training you are doing.

Carbohydrates are the preferred fuel for endurance performance, however the amount you require for each session will be dependent on its duration, intensity and type of session. Ultra-endurance maybe the exception which utilises fat as its primary fuel source, however, beyond being used as just as a fuel, adequate carbohydrates is important for recovery and can help spare muscle mass.

We can also look at manipulating your carbohydrate intake for fat loss and metabolic adaptation but this goes beyond the realms of this page.

Generally, you will need to consume around 3-5g per kg of (target bodyweight per day for lighter activity and potentially up to 10-12 for extreme programming. The summary of these recommendations from the IOC can be found on the table below. If weight loss is a factor, then aim for the lower end of the figures.

For more accurate fuelling strategies, using VO2Max testing, we are able to calculate how many carbohydrates you need during different intensities. This can be an incredibly powerful tool for fuelling training and race. Contact your sports nutritionist today for more information.


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