If like me you joined the fitness world and saw all these posts about macros and IIFYM and thought “what in the hell is all this about!” Worry no further for here it is all explained nice and simple in one place!

IIFYM or “if it fits your macros” is a way of monitoring (or controlling I suppose) what you’re eating while trying to make progress and achieve a certain goal. “But isn’t that what counting calories is for” I hear you ask well yes and no. The idea behind macros is that instead of counting calories you count Protein Fats and Carbohydrates so you could end up eating more on an IIFYM diet than you would just calorie counting. Here comes the tricky part.

Macros are worked out using maths (ew) and you can do it yourself or there are plenty of sites on the internet that will do it for you. However if like me you want to know a little bit more of the technical stuff to wow your new gym mates with then these are the basics:

First you need to calculate your REE or resting energy expenditure – this is the energy your body uses up just keeping all your organs going.

REE = 5 x weight (kg) + 6.25 x height (cm) – 5 x age (years) 

So for example a 5ft10 21 year old female weighing 72kg would have an REE of 1426.6. This is then used to calculate your TDEE – Total daily expenditure, so this now includes energy you burn through exercising.


Here Y is a number determined by how active you are in daily life. So if you are active for less than an hour a week Y=1.1. If you’re active for 1-3 hours a week Y=1.2, if your active time is more like 4-6 hours Y=1.35 and if you are a super active person (6+ hours of activity per week) Y=1.45.

Continuing my earlier example, say this female is active for 4-6 hours a week her TDEE would be 1925.91 calories.

This is then used to calculate how much Fat and Carbohydrate you should aim for per day. Protein is done purely on weight. Protien is essential for muscle growth and repair so if your aim is #GAINZ then you need to pay close attention to your Protien intake. You are very unlikely to see muscle growth without Protein. Here’s the maths:

Protein = 0.825 x weight

Fats = (TDEE x 0.25) / 9

Carbohydrates = (Protein x 4 + Fats x 9 – TDEE)/4

Using our example and the standard macro abbreviations ( P for protein, F for fats, C for carbs) our girl would have the following maintenance – more on this in a minute – macros  P 130g F 53g C 309g

Why have I times the protein by 4 and fat by 9? To get the ratio of calories right per gram (I won’t go into this just accept it is how it is ok you can use google if you really have a burning need to know).

I referred to these as maintenance macros… what does that mean?

To understand this it is important to understand the concept of calories in versus calories out. If your aim is to lose fat (not weight because remember muscle weighs more than fat so the scale doesn’t mean everything!) you need to be using more calories than you are taking in so aim for 75-80% of your TDEE. This applies to both macros and calorie counting. If you are quite happy the way you are then stick to you TDEE for calories and your maintenance macros. If you want to gain weight i.e. You are on a bulk (again #GAINZ) then you want to be eating more than you are expending so in this case eat 110-115% of your TDEE.

Phew now that we have all that mathsy science nonsense out of the way lets get to the important stuff! If the maths really isn’t your thing I have linked some macro calculators at the bottom of this post (you’re welcome).


The simple answer… there isn’t one! Some people swear by it others make great progress through just eating intuitively. Just remember the golden rule:

To LOSE fat you must be in a CALORIE DEFICIT and to GAIN fat you need to be in a CALORIE SURPLUS

Personally I think macros is not necessary unless you are a proper fitness fanatic and working towards serious muscle gain and competition style results. That being said having an awareness of them is no bad thing. Calorie counting is a much easier way to track your eating habits. I do currently track calories but I’m very on and off with it because having done it for a while I am much more aware of what I can eat day to day. I would recommend tracking either macros or calories or both for maybe a month just to get you into the mindset and then try intuitive eating. Apps like MyFitnessPal are a brilliant way to track calories and if you haven’t already I would download it.

It is also important to remember that everyone is different, and what works for someone else might not work for you which is why it’s important not to compare your progress to other people.


Another very common feeling. More muscle means a faster metabolism so during a cut progress will be much more visible. This is why a lot of people use the bulk and cut method. During the bulk phase you gain muscle which then helps with the cutting phase. So that famous fitstagrammer who suddenly has amazing abs after cutting for a month is not a good comparison to you if you’re just starting out. Progress takes time and patience!


Katy Hearn Fit macro calculator

Legion – how to calculate your macros in 5 steps

IIFYM calculator



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