Macros Calculator

The one that lets you build your own

Of the macro tools on this site, this is the one that hands you the controls. It asks for a goal, which is where it differs from our Macronutrient Calculator, and then it lets you either pick a ready-made split or type your own three percentages, which is where it differs from everything else.

That last option is the interesting one. Type any three numbers you like and the calculator will build a day around them. Which is either useful freedom or a loaded weapon, depending on whether you know what the numbers mean. So before you use the custom box, this page is going to explain the one thing that makes macro percentages behave in a way almost nobody expects.

Why 70 percent fat is not 70 percent of your plate

Pick the keto preset here and it says 5 percent carbs, 25 percent protein, 70 percent fat. Read that as a plate and you picture something horrifying: nearly three-quarters of your dinner being butter.

That is not what it means, and the reason is one small fact doing enormous work. Percentages of what? Not of your food. Of your calories. And the three macronutrients do not carry calories at the same rate. Carbohydrate and protein give you 4 calories per gram. Fat gives you 9, more than double.

So a slice of calories buys you far less fat by weight than it buys carbohydrate or protein. Run both extremes of this tool at 2,000 calories a day and watch what happens:

Look at the last two columns. A diet advertised as 70 percent fat is about half fat by weight. A diet advertised as 20 percent fat is only a tenth fat by weight. In both cases the number on the label is roughly double the reality on the plate.

This is worth internalising, because it dissolves a lot of anxiety in both directions. The keto number is less extreme than it sounds. And the low-fat number is more extreme than it sounds: a fifth of your calories from fat is a genuinely small amount of visible fat on your food, which is why very low fat diets feel so joyless to cook for. If you are going to type your own percentages, this is the fact that will stop you writing something silly.

The high protein preset asks for more than anyone recommends

Now something we found by running the tool's own presets and checking them, which you deserve to know before you pick one.

Take a 28 year old man, 178 cm, 82 kg, training 3 to 5 times a week and wanting moderate weight loss. His maintenance comes out around 2,786 calories, a 20 percent cut puts his target at roughly 2,229, and choosing the high protein split of 20/50/30 gives him this:

Two hundred and seventy-nine grams of protein. That is about 3.4 grams for every kilogram he weighs, and it is roughly a kilogram of chicken breast a day, every day, before he has eaten anything else.

Put it against the official guidance and it does not fit. The Institute of Medicine's Acceptable Macronutrient Distribution Range puts protein at 10 to 35 percent of energy. This preset sits at 50, which is not near the ceiling, it is half again beyond it. And 3.4 g/kg is well past what mainstream sports nutrition suggests even for someone lifting hard in a deficit trying to protect every gram of muscle.

Is it dangerous? For a healthy person with healthy kidneys, probably not, and protein is famously filling, which is part of why high-protein diets work for people. But it is not free either. Every one of those calories spent on protein is a calorie not available for the carbohydrate that fuels your training or the fat that runs your hormones, and at 111 g of carbohydrate a day this man is going to notice his last few sets. If you want a protein-forward diet, the honest advice is to use the custom box and put protein somewhere in the 25 to 35 percent band rather than taking the preset at its word.

Custom, and the arithmetic it enforces

Choose custom and three boxes appear. Here is what the tool will and will not let you do.

It checks that each figure sits between 0 and 100, and it checks that your three numbers add up to 100. If they do not, it stops and tells you. That sounds obvious and it is a genuinely useful guard, because the single most common mistake with a custom split is writing three numbers that sound reasonable individually and sum to 115.

What it will not do is tell you whether your split is sensible. It has no opinion. Type 5, 5, 90 and it will hand you the grams without comment. So the judgement stays with you, and the two sections above are the equipment you need for it: remember that the percentages are of calories rather than food, and remember that the official ranges run 45 to 65 for carbohydrate, 10 to 35 for protein and 20 to 35 for fat. Going outside them is a decision rather than a mistake, but it should be a decision.

If you would rather see what those official ranges look like in grams for you specifically, our Macro Calculator reports them directly and explains why they are so wide.

Two things worth knowing before you pick

The 40 percent option is a lot. The goals list runs 10 percent below maintenance, 20 percent, then 40. That last jump is not a gentle progression. For our example above, 40 percent takes him from 2,786 down to about 1,672 calories while he is still training five times a week. It is technically a faster route, and it is also the option most likely to cost him muscle, wreck his training and end in a fortnight. The tool will hold at a floor of 1,500 calories for men and 1,200 for women rather than going lower, but a floor is a last line of defence, not a recommendation. Mild or moderate is the right answer for almost everyone. Our Calorie Deficit Calculator explains why patient beats aggressive.

There is a gap in the activity list. The dropdown offers sedentary, then jumps straight to moderate, meaning exercise 3 to 5 times a week. There is no option for the very common case of training once or twice a week. If that is you, you are stuck choosing between a factor that assumes you do nothing and one that assumes you train most days, and the gap between them is worth a few hundred calories. Pick sedentary and treat the answer as a floor, or use our TDEE Calculator, which has the full ladder, and bring the number back here.

Questions people ask

What is a good custom split?

For most people wanting to lose fat while keeping muscle, something around 40 percent carbohydrate, 30 percent protein and 30 percent fat is a sane place to start. It sits inside official guidance apart from carbohydrate being marginally low, it gives you plenty of protein without absurdity, and it leaves enough fat to cook properly.

Why will it not accept my numbers?

They must add up to 100, because they are shares of the same pot of calories. If your three figures sum to anything else, the tool cannot split your day with them.

Does the split actually matter that much?

Less than the calorie target above it, and much less than whether you stick to either. Protein is the one worth getting roughly right, because it protects muscle while you lose. Beyond that, choose what you can eat.

What does the build muscle option do?

It adds 500 calories to your maintenance. Note that this is a flat figure rather than a percentage, so it is a much bigger surplus for a small person than a large one. Our Calorie Surplus Calculator scales the surplus to your size instead, and explains why a bigger one does not build more muscle.

References

Where the figures come from. The energy values of 4 calories per gram for carbohydrate and protein and 9 for fat, and the Acceptable Macronutrient Distribution Ranges used to judge the presets above, are from the Institute of Medicine's Dietary Reference Intakes work on energy and macronutrients. The resting equation the tool runs is Mifflin-St Jeor, and the systematic review finding it the most accurate of the common resting equations is Frankenfield and colleagues.

1. National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Energy. Washington DC: The National Academies Press. https://www.ncbi.nlm.nih.gov/books/NBK591020/
2. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington DC: The National Academies Press; 2005. Acceptable Macronutrient Distribution Ranges: carbohydrate 45-65%, fat 20-35%, protein 10-35% of total energy.
3. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. 1990;51(2):241-247. https://doi.org/10.1093/ajcn/51.2.241
4. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. 2005;105(5):775-789. https://doi.org/10.1016/j.jada.2005.02.005