Macro Calculator

Why does this one give you a range?

Ask the internet what your macros should be and you will get a number, delivered with total confidence. Forty, forty, twenty. Or thirty, forty, thirty. Whichever it is, it will be precise, and the person telling you will not seem troubled by the fact that the last person told you something different.

Set this tool to Maintain Weight and it does something unusual. It refuses to pick. It hands you back three ranges: so many grams of protein to so many grams, and the same for carbohydrate and fat. That can feel like a cop-out, like the calculator could not be bothered to decide.

It is the opposite. Those ranges are the official answer, and the official answer really is a range. It is the confident single number that is making things up.

The ranges are enormous, and that is the finding

Look at what the tool actually gives you. Protein is 10 to 35 percent of your energy. Carbohydrate is 45 to 65 percent. Fat is 20 to 35 percent.

Take the protein one seriously for a moment, because it is startling. The top of that range is three and a half times the bottom. On a 2,000 calorie day it means anything from 50 g of protein to 175 g. Both ends are officially fine. That is not a rounding tolerance or a margin of error; it is an admission, printed by a national scientific body, that across a span that wide the evidence does not let them pick a winner.

So when the next article tells you there is one correct macro split and helpfully sells you a plan built on it, you now know how to place that claim. The people who reviewed the entire literature could not narrow protein below a three-and-a-half-fold span. Somebody with an app has not resolved what they could not.

This is liberating rather than annoying. It means the split is not the thing that decides your outcome. Your total calories decide most of it, and after that, whichever split you can actually live with and eat consistently beats the theoretically optimal one you abandon in March. Pick a point in the range that suits your food, your budget and your cooking, and stop worrying about the decimal.

Where the ranges came from

These are the Acceptable Macronutrient Distribution Ranges, and they were set by the Food and Nutrition Board of the Institute of Medicine for planning and assessing the diets of healthy people.

The reasoning behind the edges is worth knowing, because it explains the shape of the thing. The board went looking for the points at which a macronutrient starts to be associated with chronic disease. They put the carbohydrate ceiling at 65 percent because heart disease risk appeared to rise above it. They put the floor at 45 percent because pushing carbohydrate lower means pushing fat higher, and very fat-heavy diets are extremely energy dense, which they linked with obesity risk. Protein got its range partly by subtraction: once you have covered the minimum the body needs and left room for the other two, the flexible remainder is large.

Two honest footnotes. First, these ranges were published in the early 2000s and have not been revised since, so they are a settled consensus rather than a fresh one. Second, they are ranges for reducing chronic disease risk in healthy people. They are not performance targets, and an athlete chasing muscle will reasonably sit at the protein end that a sedentary person does not need.

The one calculator here that will tell you no

Now the part of this tool we are quietly proud of.

Switch the goal to Change Weight and it asks for a target weight. Then, before it plans anything, it works out what BMI that target would put you at. If the answer is 25 or above, or below 18.5, it stops. No plan, no macros, no timeline. Just a note that the target you typed would leave you overweight or underweight, that this may pose a threat to your health, and that you might want to reconsider.

Out of every calculator on this site that accepts a goal weight, this is the only one that does that. The others will take any number you give them and cheerfully compute a route to it. This one reads your target and, when the target is a bad idea, declines the job.

You may find that irritating, and it is easy enough to work around by typing a different number. But we would rather have a tool that occasionally refuses than one that will help you plan anything at all without comment. If the warning has appeared and you are not sure what a sensible target would be, our Healthy Weight Calculator will show you the range for your height.

If you chose Change Weight

Assuming your target passed that check, here is what happens. The tool works out your maintenance calories from the Mifflin-St Jeor equation and your activity level, then adjusts them by your chosen pace.

The pace options are 0.5 kg a week or 1 kg a week, and they are converted using the standard rule that a kilogram of body fat is worth about 7,700 calories. So half a kilogram a week works out at 550 calories a day, and a kilogram a week at 1,100 a day. That second one is a large daily gap, and worth respecting. If a weight-loss target would drop you below the guideline floor, the tool holds at 1,500 calories for men and 1,200 for women rather than going lower. Those figures are the bottom of the range the 2013 AHA/ACC/TOS obesity guideline prescribes, rather than a line between safe and unsafe.

Two honest notes on the timeline it gives you. It assumes every kilogram you shift is fat, which is not what happens, particularly in the early weeks. And it assumes your maintenance stays put as you change, which it does not. Our Calorie Deficit Calculator explains why the first fortnight misleads, and our Kg to Calorie converter explains where the 7,700 comes from.

Questions people ask

So what is the best macro split?

There is no single answer, and that is a finding rather than a dodge. Anything inside the official ranges is defensible for a healthy adult. Choose by what you can eat consistently.

Why does the tool give ranges for Maintain but a single figure for Change Weight?

Because Maintain has no goal to aim at, so it reports the official ranges. Once you set a target weight the tool has something specific to solve for, so it commits to a number.

Is it bad to eat outside these ranges?

Not automatically, and plenty of people do. The ranges describe where chronic disease risk looks lowest across a population of healthy adults. Going outside them, as low-carb and keto diets do, is a decision worth making deliberately rather than by accident.

The tool refused my target weight. Can I override it?

Not within the tool, no. It will only plan toward a target that lands in the healthy BMI range. If you believe your target is right for reasons a BMI cannot see, such as carrying a lot of muscle, that is a conversation worth having with a doctor or dietitian rather than a calculator.

References

Where the figures come from. The Acceptable Macronutrient Distribution Ranges, and the reasoning behind where their edges sit, are from the Institute of Medicine's Dietary Reference Intakes report on energy and macronutrients. The National Academies' more recent Dietary Reference Intakes work is the current home of that guidance. The resting equation the tool runs is Mifflin-St Jeor.

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