Macro Calculator

How the split is calculated

Most macro calculators start with three percentages (40/30/30, say) and slice your calorie budget into them. This one does not. It fixes protein first from your body weight, fixes fat second as a share of calories with a hard floor underneath it, and gives carbohydrate whatever energy is left. The order matters, and it is the whole argument of this page.

The energy values behind those divisions are the Atwater factors used on every food label in the world: protein and carbohydrate supply about 4 kcal per gram, fat about 9. They are rounded averages of digestible energy, not physical constants, which is one small reason the arithmetic on this page should never be treated as precise to the gram.

Why protein is anchored to body weight, not to a percentage

A percentage-based protein target has a failure mode that shows up at exactly the worst moment. Suppose you set protein at 30% of calories. At 2,600 kcal that is 195 g for a 75 kg person, which is generous. Now cut to 1,500 kcal for a hard fat-loss phase and the same 30% delivers 113 g, or 1.5 g/kg. Your protein requirement did not fall when you started dieting. If anything it rose, because a calorie deficit is precisely the condition under which the body starts breaking down muscle for fuel, and dietary protein is the main thing standing in the way. The percentage approach cuts your protection at the moment you need most of it.

Anchoring protein to body weight removes that failure. Your lean mass does not care what your calorie ceiling is this week, so the target does not move when the deficit deepens. The practical consequence is that on an aggressive cut, protein ends up occupying a large share of a small budget, sometimes 40% or more of total calories. That is not a mistake in the arithmetic. It is the point.

The specific number comes from a 2018 meta-analysis by Morton and colleagues, pooling 49 studies and 1,863 participants on protein supplementation and resistance training. Gains in lean mass rose with protein intake and then flattened: the breakpoint fell at roughly 1.62 g/kg per day, with a confidence interval reaching to about 2.2 g/kg. That is where this calculator's 1.6–2.2 g/kg band comes from. Below 1.6 you are likely leaving results on the table; above 2.2 the evidence for further benefit thins out considerably, though higher intakes are not harmful in healthy people.

Sources: Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med 52:376–384 (2018). Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr 14:20 (2017). Fat floor per Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids (2005).

The four diet styles compared

The four presets differ in two settings only: how much protein per kilogram, and what share of calories comes from fat. Carbohydrate is never set directly. It is whatever remains once the other two are paid for, which is why the carb column below moves so much while the protein column barely does.

Here is the honest version of what the research says about choosing between them: for fat loss, the calorie total and the protein figure do essentially all of the work, and the carb-to-fat ratio does almost none. Controlled feeding studies that hold calories and protein constant while swinging carbohydrate and fat across a wide range find fat loss differences that are small and often statistically indistinguishable from zero. Low-carb diets frequently win short trials, but largely because they were not calorie-matched, and because early water-weight loss inflates the scale reading in the first fortnight.

What genuinely differs between the styles is how easy they are to live with, and that is not a trivial consideration. It is the whole game. A split you follow for eight months beats a theoretically superior one you abandon in three weeks. Some people feel steady and unbothered by hunger on high fat and low carbohydrate; others feel flat, sleep badly and cannot finish their training sessions. Neither reaction is a character flaw or a metabolic peculiarity. Pick the one you can actually eat, and treat the preset as a starting shape rather than a rule.

One caveat specific to training: if you do repeated high-intensity work (intervals, team sports, anything over about 75% of maximum effort for sustained periods), carbohydrate availability does affect performance, and very low intakes tend to cost you. Endurance work at conversational pace is far less sensitive. If your training is mostly hard and glycolytic, the balanced or high-protein presets will serve you better than keto will.

Where these numbers mislead

The ranges here describe healthy adults with normally functioning kidneys and liver. That qualifier does real work. In chronic kidney disease, protein intake is often deliberately restricted, and the appropriate figure depends on the stage of disease and whether you are on dialysis. It is set by a renal dietitian, not by a calculator that knows only your weight. Liver disease, some inherited metabolic disorders, and pregnancy all shift the targets in ways no general-purpose tool can model. If any of those apply to you, treat this page as background reading and nothing more.

There is a persistent claim that high protein damages healthy kidneys. The evidence does not support it: controlled trials and long-term observational work in people with normal renal function have not shown harm at the intakes discussed here. The measured rise in glomerular filtration rate that follows a protein meal appears to be a normal adaptive response rather than injury. Existing kidney disease is the real caveat, and it is a serious one.

Then there is measurement error, which is almost certainly larger than the difference between any two splits on this page. Nutrition labels are legally allowed to be wrong: in the United States the FDA treats a label as compliant if the measured value is within 20% of the declared figure for nutrients like fat, and EU tolerance guidance is comparably wide. Portion estimation adds more error on top. Studies of self-reported intake routinely find under-reporting of 20% or more, concentrated in exactly the foods people would rather not write down. Cooking method, drainage, and the fat left in the pan all move the real number.

Put those together and the practical conclusion is deflating in a useful way. Your true intake on a day you recorded as 150 g of protein and 60 g of fat might genuinely have been 135 g and 72 g. Against that noise, agonising over whether fat should be 28% or 30% is not a good use of your attention. Get the calorie total roughly right, get protein consistently near target, and let the rest sit where it lands.

Finally, the calorie figure this page starts from is itself an estimate. The Mifflin-St Jeor equation predicts resting metabolic rate within about 10% for most people, and activity multipliers are blunter still. Our TDEE calculator goes into that uncertainty properly. The only real calibration is two or three weeks of consistent eating and weekly weigh-ins: if the scale is not moving the way the arithmetic predicted, the arithmetic was wrong about you, and the number to change is calories.

Hitting the numbers in practice

A daily protein total is easier to hit if you spread it across meals rather than chasing it with a large evening portion. Muscle protein synthesis responds to a per-meal dose rather than a 24-hour total, and the response saturates somewhere around 0.4 g/kg in a single sitting, roughly 30 g for a 75 kg person, more for larger or older people. Three or four meals each carrying a real protein source will get you there with less effort than two meals and a scramble at bedtime. The calculator shows your per-meal figure across four meals for exactly this reason.

Older adults need a larger per-meal dose to trigger the same response, an effect usually called anabolic resistance. If you are over about 60, aim for the upper end of the protein range and make sure breakfast carries a proper share of it. That is the meal most likely to be protein-light in a typical Western diet.

Why the fat floor exists

Below roughly 0.6 g per kilogram of body weight, dietary fat starts causing problems that have nothing to do with calories. Fat is the carrier for vitamins A, D, E and K, so an extremely low-fat diet quietly impairs their absorption. The essential fatty acids, linoleic and alpha-linolenic, cannot be synthesised at all and must come from food. And sustained very low fat intake during a calorie deficit is associated with falling sex hormone concentrations in both men and women, with the downstream effects on mood, libido, menstrual regularity and recovery that implies.

The floor mostly bites on aggressive cuts at low body weight, where a fat percentage that is perfectly sensible at maintenance calories produces too few actual grams. This calculator surfaces that case as a visible warning rather than quietly handing you a number that looks fine on a chart. The fix is straightforward: raise the fat share, accept fewer carbohydrates, or raise calories and extend the timeline.

Fibre, and what the calculator does not split out

Carbohydrate is a single line here, but the composition of it matters more than the total. The reference intake for fibre is around 14 g per 1,000 kcal, roughly 28 g on a 2,000 kcal diet, and most people fall well short. Fibre affects satiety, glycaemic response and gut health, and a carbohydrate target hit entirely with refined sources will feel very different from the same number reached through legumes, oats, fruit and vegetables. Your fibre figure appears in the results panel above.

Two other things sit outside this tool's scope. Alcohol supplies about 7 kcal per gram and belongs to none of the three macronutrients; if you drink, it comes out of the carbohydrate and fat budget in practice. And micronutrients are invisible to a macro split entirely. You can hit every gram target for a month on a diet that is short on iron, calcium or vitamin D. A macro calculator is a framework for energy and body composition, not a complete account of eating well.

If you want to work through the numbers underneath this page, start with your total daily energy expenditure, and check your body fat estimate if you carry unusually high or low lean mass, since protein targets scale better to lean mass than to scale weight at the extremes.

Common questions