How many calories should you be eating per day? What about if you’re looking to burn fat? How should those calories be split between protein, fat and carbohydrates? These aren’t rhetorical questions; if you want to take your weight loss seriously, you might need to know these numbers.

This is especially true if you’re looking to lose weight through managing your macronutrients (sometimes called macros). This term refers to the main nutrients that make up what you eat: protein, carbohydrates and fat. Many people have experienced weight loss success through eating specific amounts of these each day.

Luckily, there are a few methods to work these out. If you want to calculate your macros — or just want to know how many calories your metabolism naturally burns each day — then all you need to do is a few calculations. And we’re here to show you how.


Working out your BMR

The first thing you’ll need to do is calculate your basal metabolic rate (BMR), which is simply how many calories your body naturally burns on its own to digest food, keep you awake, and provide your muscles with the energy they need to keep you moving. There is a mathematical formula to work this out, depending on whether you’re a man or a woman:


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

Women: BMR = (10 x weight in kg) + (6.25 x height in cm) — (5 x age in years) — 161


So, let’s say you’re a 25-year-old woman who is 162 cm tall, and who weighs 61 kg. Your weight multiplied by 10 would be 610; your height multiplied by 6.25 would be 1,012.5; and your age multiplied by 5 would be 125. That means our equation is:


BMR = 610 + 1,012.5 — 125 — 161


We add the first two numbers together, giving us 1,622.5. Next, we take away 125, giving us 1,497.5, then we take 161 away from that, giving us our final basal metabolic rate of 1,336.5.

This is how many calories your body would burn each day if all you did was lie perfectly still. However, you almost certainly have a more active lifestyle than that, so we are going to need to modify our calculations slightly…


Activity level

To get a more accurate number, you need to work out what your activity level is. There are four options here: little exercise, light exercise, moderate exercise and heavy exercise. If you don’t really exercise and you have a desk job, you probably fall into the first category.

If you exercise between one and three times per week, you would count in the light exercise categories. Three to five times would bump you up to moderate, and six or seven would mean you’d count as heavy. You can move yourself up or down a category if the exercise you do is particularly intense, or if it’s fairly easy-going.

Each activity level has a number associated with it, which you can multiply your BMR by in order to get an accurate picture of the calories. They are as follows:

  • Little exercise: 1.2
  • Light exercise: 1.375
  • Moderate exercise: 1.55
  • Heavy exercise: 1.725

So let’s go back to our example above, of a woman with a BMR of 1,336.5. If she falls into the light exercise category, we’d multiply this number by 1.375. This gives us a total of 1,837.7, which is the amount of calories our hypothetical person should be aiming for.


Splitting this into macronutrients

Most people who start out on the macronutrient method of dieting opt for a 40-40-20 split; that means 40 per cent of their diet will be made up of protein, 40 per cent will be carbohydrates, and 20 per cent will be fat. You can use these numbers to work out how many calories of each you should be eating per day.

Going back to our example, we’d worked out they should be eating 1,837.7 calories each day. We can work out 40 per cent of this by multiplying it by 0.4, and work out 20 per cent by multiplying it by 0.2. This works out as 735.1 calories from protein, 735.1 from carbs, and 367.5 from fat.

To make it easier, we can convert these calories into grams, as this is what you’d see on the back of most food packets. To do this for protein and carbs, divide the number of calories by four. To do it for fat, divide it by nine. So to finish off our example, she’d need to eat 183.8g of carbs and protein each day, and 40.8g of fat.

It might seem tricky at first, but if you follow this process you’ll be able to work out an accurate number for the macronutrients you should be eating each day.