How to set your macro ratios

The ratio is an output, not a target

The macro question almost always arrives as a percentage. Yet the percentage is what the calculation produces, not what it consumes. Your protein and fat needs are defined in grams per kilogram of body weight; put those two in place and carbohydrate fills whatever room is left, with the percentages forming on their own.

One example runs through the page: someone weighing 75 kilograms who is aiming at 2,000 calories a day. At 1.8 grams of protein per kilogram that is 135 grams, and at 0.8 grams of fat per kilogram it is 60 grams. Together they come to 1,080 calories, so the remaining 920 calories become 230 grams of carbohydrate.

The ratio that appears is 27% protein, 46% carbohydrate, 27% fat. Nobody chose it. It came out of three gram figures and a single calorie target.

Same grams, three different percentages

Hold the same person’s protein and fat grams still, move only the calorie target, and the table looks like this:

Every row carries 135 grams of protein and 60 grams of fat. The body’s requirement never changed and the grams on the plate never moved, yet the protein share fell from 34 to 22 and the carbohydrate share climbed from 33 to 57. That 24-point swing in carbohydrate is not a nutrition decision; it comes from the denominator.

Borrowing someone else’s ratio means borrowing their calorie target without noticing.

A fixed percentage cuts protein at the worst moment

The reverse direction matters more. Fix the percentage and move the calories, and the grams get dragged along behind the percentage, which works against you precisely when you are dieting.

Take the same 75-kilogram person holding protein at 30%. At 2,500 calories that is 187 grams, or 2.5 grams per kilogram, comfortably above what is needed. Drop to 1,600 and the same 30% delivers only 120 grams, down to 1.6 per kilogram.

Protein requirements do not fall in a deficit. They rise. Protein is the strongest lever you have for holding on to muscle while calories are restricted, and a fixed percentage pulls it down over exactly that stretch. How much protein you need in a day is a separate article; the point here is that the number belongs to your body weight rather than to a share of your calories.

Fat has a floor underneath it

Of the two remaining macros, fat is not compressible space. Your body cannot make certain fatty acids on its own, vitamins A, D, E and K are absorbed only when fat is present, and steroid hormones are built from the same raw material.

Half a gram per kilogram, or 20% of total calories, works as a practical lower bound. On the example body that lands somewhere between 38 and 44 grams.

Going under that line stops being a matter of preference. Carbohydrate sits differently: the body can manufacture glucose when it has to, which makes carbohydrate the macro that genuinely stretches.

Why the popular ratios contradict each other

40/40/20, 50/30/20, a ketogenic split. They answer the same question in wildly different ways and all of them appear to have worked somewhere.

In controlled trials where both calories and protein are matched, the difference in fat loss between low-carbohydrate and low-fat patterns comes out small. What separates them is not the ratio itself but how many weeks a person can keep eating that way.

The large difference visible in the first weeks is mostly water. Every gram of stored glycogen holds roughly 3 grams of water alongside it, so anyone cutting carbohydrate sharply sees 1 to 2 kilograms come off the scale in week one, and none of that has anything to do with fat; the same weight returns when the carbohydrate does.

What the ratio does not decide

The same 46% carbohydrate can arrive from pulses or from fizzy drinks. The ratio cannot tell them apart.

Fibre is an axis the ratio never sees. Around 14 grams per thousand calories is a widely used reference, which works out at 28 grams a day for this body. Two days can report an identical macro table while one carries 10 grams of fibre and the other 35.

Micronutrients are in the same position. A macro table shows three columns and far more than three things are happening on the plate. The ratio is a frame, not a menu.

How to build it, and when to change it

Four steps, in order. Calories first, because a ratio means nothing without a total, and where the daily calorie target comes from is that step’s own subject. Then protein per kilogram, then the fat floor, then whatever is left written down as carbohydrate.

Good reasons to change it are few. If your body weight has moved appreciably, the gram figures get recalculated. If your training volume has gone up, the carbohydrate share grows. If you keep missing one macro, the problem is not the ratio but the fact that this ratio does not fit the way you eat.

It also pays to be realistic about precision. Given the error in estimating portions, 10 grams on protein and about 20 on carbohydrate is the resolution you can actually reach. Chasing the difference between 45% and 48% is chasing something you cannot measure.

The macro calculator runs those four steps on your own numbers and reports grams alongside percentages. If the total has to be settled first, the calorie calculator handles that step. And if you want the protein side in more detail, there is the protein intake calculator.