Q&A: How do I calculate calorie and macronutrient needs?

Do you find figuring out the whole calories and grams of protein, fat and carbs confusing? In the dark about how much you should really be eating?

You’re not alone.


I was in the gym the other day having a chat with a strength and conditioning coach and trainer. They told me how they’d been playing around with calorie and macronutrient calculators, the questions that came up were basically these

I was looking into calorie and macronutrients calculators, using them I’ve come out with some crazy numbers, so,

How do you calculate numbers,
Is there any simple way of breaking it down how much protein, fat and carbs you should eat,
How do you tailor those numbers for goals, and,
How do I implement this with a client?’

This follows on nicely from the theme of first month’s diet, IIFYM, but a gym is a shitty place to pass on nutrition info, with all its various caveats and different arguments so I followed up with a short email, the edited version of which is below.

I’ve added some more info clarity and there’s some examples but if you want to skip through (for a 2-4 minute read) then stick to the underlined sections

Enjoy, it should answer most of your calorie and macro calculating questions.



Calculating the numbers

Calories and grams of carbs, protein and fat

Most calculators will start by calculating total calories needed based on body size, activity and maybe some other factors, then they’ll divide that figure up into carbs, protein and fats using either a preferred ratio – 40:30:30 calories from carbs, protein and fat for example – to then spit out the number of grams you should eat a day, others let you choose a ratio.

(Remember that the ratio is calories from the particular macro not grams.)

Always keep in mind there’s two problems here: how many total calories, and how you split those calories up, i.e. the proportions/ratios of proteins, fats and carbs

  • The calorie recommendations are based on some logic, most use one of a small number of standard tools/equations which use body stats and activity and so on, so known, measured variables.
  • The ratios are often more about personal preference and prejudices of the trainer, consultant whoever. Some like lower fat, some lower carbs for example.

A little art, a little science. This is one of the BIG reasons for the confusion when it boils down to setting grams of this and that to eat.

Four Calculators

So below are links to some calculators (one is a link to a vid that explains a tool, if you can’t get hold of that to download let me know).

I’d recommend having a play with all using the same three different examples.

IIFYM calculator:
Standard calorie calcs with a number of standard or custom options for tailoring total calories and macro ratios as well .

The Alan Aragon calculator
calculator in a spreadsheet form, a nice tool, see below for details

Precision Nutrition calculator
this is a slightly different beast, with a heavy emphasis on long term tracking, management and compliance, and well worth a look

Bodybuilding.com calculator
This is an example of a calculator wedded to the notion that there’s one optimum ratio of prot/carb/fat for everyone.



Tailoring the number to goals: Calculating macros (and total calories):

Three Methods

The the calculators above will give you a guideline but you (mostly) still have to decide what ratio of macros to use. So how do you do that?

1)  Complicated

There’s all sorts of variables that might alter what is best for a person both in terms of total calories and the proportions/ratios of macros. Many of these are health, lifestyle and age related. For example, if they’re young, very lean and have always been very lean then they can probably get away with the higher end of the calorie recommendation and certainly a bigger carbohydrate load than others might.

There’s so many ideas on what factors are involved, what weighting you give them – things like gut flora, inflammation, hormonal milieu blah blah blah – it turns into a sort of nutritional alchemy and I’m not going to start detailing them here. It’s almost pointless. In fact I know coaches/nutritionists/team Dr’s in top flight sport who after thousands of pounds worth of courses on this have just gone back to the simple methods: set a sensible start point and then monitor.

Again, calorie recommendations tend to be a little more standard, macro ratios less so, and there’s all sorts of ratios on that IIFYM calculator so have a play around, if just for interests sake.

2) The Simple Method.

Keeping things simple, a commonly accepted method which relies on simple multiples of bodyweight and sets protein reasonably high, but not crazy, fat moderate. It gives protein and fat based on bodyweight and then lets carbs control the rest of the calorie intake depending on needs. By this I mean

  • Protein: ~2 g/kg/day
  • Fat: 1g/kg/day
  • Carbs: whatever is left from the total cals minus those from protein and fat

(Fibre? … ultimately fibre contains calories however not many in total – typically 1-3kcal/g and we’re only talking around 20-40g fibre per day for most – and they’re certainly beneficial ones, these are generally ignored.)

It’s not always right, but it’s a simple start point to work with. The reason it works is because it takes account of goals, you’re altering the one non essential variable – the carbs – to account for goals and needs. But of course you still have to know your total calories.  

If someone wants to lose fat you take it away from the carbs and you’re left with a lower calorie higher protein diet which at least in the short and medium term is well supported by the literature. If someone wants to gain weight then there’s ample protein and fat and you’ll consume extra carbs which help support training and drive growth, again evidence based.

Example (this is off the top of my head so numbers are rough)

Step one is to work out the rough calorie needs based on weight and activity.

Male, 25, 80kg, 5’11″, moderately active and training 3 days a week. Bang these into a calculator such as IIFYM then you’ll get something like:

  • BMR ~1800kcal
  • TDEE ~ 2500kcal
  • Fat loss: 2000kcal
  • Muscle gain: 2750kcal

Then you work out how much protein, fat and carbs to give them. Protein and fat is simple, then the carbs make up the rest.

[remember this is an 80kg man, I am factoring 2.2g per kg for protein and 1g per kg for fat]

  • Protein: 80[kg] x 2.2 = 176g
  • Fat: 80[kg] x 1 = 80g
  • Carbs: Here you work backwards from the calories left over that aren’t protein or fat

Protein and fat total calories:

  • Protein: 80[kg] x 2.2 = 176g x 4[kcal per gram] = 704kcal
  • Fat: 80[kg] x 1 = 80 x 9[kcal per gram] = 720kcal
  • 720 + 704 = 1424

So carb cals (and grams when divided by 4) are what’s left after you take away the total of pro and fat which is 1424kcal

  • TDEE or ‘maintenance’ [where you equal the total daily energy needs]
    2500 – 1424 = 1076kcal / 4 = 269g/day
  • Fat loss [knocking off 500kcal to trigger the use of more stored body fat]
    2000 – 1424 = 576kcal / 4 = 144g/day
  • Muscle gain [eating more calories than needed to support growth]
    2750 – 1424 = 1326kcal / 4 = 330g/day

Of course it’s a just a starting point, you can and should tailor as needed, but it’s elegant, accounts for start point and goals and is pretty effective, and means that you – as the trainer with many clients – have a simple template where you just have to mess around with one number.

3) An even simpler method?


Alan Aragon, who I (and many others) have a lot of time for has quite a nice little tool he uses, which is based on goal weight. It’s uses lbs so you have to multiply your kilo weight by 2.2 of course. This method is simple, can be used for gaining and losing fat equally and also gives an easy way to calculate total carbs.

It works like this

  • Total calories per day = goal weight in lbs x (hours trained per week + 9.5)
  • Protein grams per day = goal weight in lbs
  • Fat grams per day = half goal weight in lbs
  • Carbs grams per day = the rest of the calories divided by 4


(similar to before, not the same)

Male, 25, 85kg, 5’11″, moderately active and training 3 days a week for 1 hour

Goal weight = 80kg

Step 1

Goal weight = 80kg with equals 176lb
Total calories = 176  x (3 + 9.5)
= 176 x 12.5
= 2200kcal

  • Protein = 176g/day (at 4kcal/g = 704kcal)
  • Fat = 176 / 2 = 88g/d (at 9kcal/g = 796kcal)
  • Carbs  = 2200 – (704 + 796)
    = 2200 – 1500 4
    Carbs g= 700 / 4
    = 175g per day.

So broadly similar numbers as per my method above.

So there’s three ways to look at it.

  1. Go on a number of crazy expensive courses looking at incredibly complex ways of setting cals and macros
  2. Use the online calculators like the ones linked above
  3. Use a calorie calculator and then the grams per kilo or lb bodyweight as per the last two examples

Then there’s the problems when the numbers meet the real world, the fourth bit of the question. Which is coming in the next blog.

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