How to Set Your Macros: A Practical Guide

Calories decide whether you gain, lose, or maintain weight. Macros — protein, carbohydrates, and fat — decide what that weight is made of, how you perform, and how hungry or satisfied you feel getting there. Once you know your daily calorie target, splitting it into macros is what turns a number into an actual eating plan.

What each macro actually does

Protein is the building block for muscle, and it's also the most satiating macro — meaning it keeps you fuller for longer per calorie than carbs or fat. It matters most when you're in a calorie deficit, since adequate protein is what signals your body to hold onto muscle instead of burning it for fuel alongside fat.

Carbohydrates are your body's preferred and most readily available fuel source, particularly for higher-intensity exercise. They're not "bad" or optional for most people — restricting them too aggressively is one of the main reasons low-carb diets feel hard to sustain during training.

Fat is essential for hormone production, including testosterone and estrogen, and for absorbing certain vitamins. Going too low on fat for extended periods can affect hormonal health, which is why every reasonable macro split keeps a meaningful floor of fat intake regardless of goal.

Grams vs. calories

Protein and carbs both provide 4 calories per gram, while fat provides 9 calories per gram — more than double. This is why a "40% fat" split looks smaller in grams than a "40% carb" split at the same calorie percentage: fat packs more energy into less food weight. FitCalc's macro calculator does this conversion for you, turning your percentage split into actual grams to hit.

Choosing a split

• Balanced (40/30/30) — a solid default for general fitness and maintenance, without leaning hard in any direction.
• High-protein (40/40/20) — useful when you're in a calorie deficit and want to protect muscle mass, or when you're training for strength and want to maximise recovery.
• Low-carb (35/15/50) — suits people who feel better, more stable, or less hungry on fewer carbohydrates, though it's a preference rather than a requirement for fat loss.

None of these is objectively "correct." The best split is the one whose food you'll actually eat consistently for months, not the one that looks most optimal on paper for two weeks.

You don't need to hit these exactly

Precision matters far less than consistency. Landing within roughly 10–15 grams of each target on most days will get you the same practical results as hitting the numbers exactly every single day. Treat your macro targets as a compass, not a courtroom.

Protein: set this one first

If you only get one macro roughly right, make it protein. It's the macro with the strongest evidence behind a specific target, and the one where falling short has the clearest consequences — particularly in a calorie deficit, where adequate protein and resistance training are the two main things preserving muscle while you lose fat.

Research across sports nutrition converges on roughly 1.6 to 2.2 g per kg of body weight per day for people training regularly. Below about 1.6 g/kg, the muscle-preserving and muscle-building response tends to fall off. Above roughly 2.2 g/kg, studies generally stop showing additional benefit for most people — the extra isn't harmful in healthy individuals, it simply stops adding anything. If you're carrying a lot of body fat, basing the figure on a target or lean body weight rather than total weight avoids inflating the number unnecessarily.

Distribution matters less than people think, but it isn't irrelevant. Spreading intake across three or four meals containing 25–40 g each tends to work slightly better than one very large serving and two small ones, and it's usually easier to manage anyway.

Fat has a floor, carbohydrate takes the remainder

Dietary fat isn't only an energy source — it's required to absorb vitamins A, D, E and K, and it supports hormone production. Cutting it very low to make room for other macros tends to backfire. A practical floor is around 0.6–0.8 g per kg of body weight, or about 20% of total calories, whichever is higher. Going below that for extended periods is where people tend to run into problems with energy, mood, and in some cases menstrual regularity.

Carbohydrate then takes whatever calories are left. It's the macro with the least strict requirement — the body can manufacture the glucose it needs — but it's also the primary fuel for hard training. Low-carbohydrate approaches can work perfectly well for fat loss, and some people strongly prefer them, but high-intensity and high-volume work usually suffers on very low intakes. If your sessions feel flat and your weights are falling, carbohydrate is the first thing to look at.

Fibre: the one that isn't on the chart

Fibre is technically a carbohydrate and rarely appears in a macro split, but it affects how a diet feels more than almost anything else on the list. UK guidance recommends around 30 g a day, and most adults fall well short. In a calorie deficit it earns its place twice over: high-fibre foods are bulky and slow to eat, so they blunt hunger considerably at a given calorie cost, on top of the digestive and cardiovascular benefits.

When a split needs changing

Macro targets aren't permanent settings. Worth revisiting when your calorie target changes materially, when training volume shifts, or when something isn't working — persistent hunger often points at too little protein, fat, or fibre; flat sessions often point at too little carbohydrate; and a diet you keep abandoning by Thursday usually points at a split that doesn't match how you actually like to eat. The best split is the one you'll follow, and a theoretically optimal plan you can't sustain loses to a decent plan you can.

This guide is for general education and planning, not medical or dietetic advice. If you have a medical condition affected by diet, consult a registered dietitian or doctor before making significant changes.