About the Macro Calculator
Splitting calories into protein, carbohydrate and fat. The arithmetic is trivial — 4 calories a gram for protein and carbohydrate, 9 for fat — so this macro calculator spends its effort on the two things that arithmetic hides.
A percentage is the wrong unit for protein.
The calories on the label are not the calories you keep.
Both are quantifiable, and both change what you should actually do.
How to Use the Macro Calculator
Enter your daily calories — from the calorie or TDEE calculator, or your own target.
Enter your bodyweight, which is what protein is actually checked against.
Pick a split, or set your own percentages.
Step-by-Step Example
2,000 calories, 80kg, balanced 30/40/30.
Protein: 2,000 × 30% ÷ 4 = 150 g
Carbs: 2,000 × 40% ÷ 4 = 200 g
Fat: 2,000 × 30% ÷ 9 = 67 gThat protein figure is 1.88 g per kilogram of bodyweight, which clears the 1.6 generally considered adequate. Good — but notice that the split did not guarantee it. The bodyweight did.
Why Protein Should Not Be a Percentage
Protein requirements scale with your body, not with your dinner.
A 30% split of 2,500 calories is 188g. The same 30% of 1,400 calories is 105g. Same split, and for a 95kg person the second is well short.
Worse, this fails in exactly the wrong direction: the same percentage delivers less protein as calories fall — precisely when a deficit makes protein most important for holding on to lean mass.
95 kg person, 1,400 calories, endurance split (20% protein):
70 g of protein = 0.74 g/kg
Adequate is 1.6 g/kg
Which would need 43% of these caloriesForty-three per cent. The split that looked reasonable as a percentage is less than half of what it should be in grams, and no amount of staring at "20%" would tell you.
The calculator converts to g/kg and says so directly.
| Target | g per kg |
|---|---|
| Low | 1.2 |
| Adequate | 1.6 |
| In a deficit or training hard | 2.2 |
For an 80kg person that is roughly 128g to 176g a day.
The Label Is Not the Net
Digesting food costs energy — the thermic effect of food — and it costs dramatically different amounts by macro:
| Macro | Cost to digest |
|---|---|
| Protein | ~25% |
| Carbohydrate | ~8% |
| Fat | ~2% |
So two diets of identical calories do not deliver identical energy.
2,000 calories, 40/30/30: 260 lost to digestion → net 1,740
2,000 calories, 15/55/30: 175 lost to digestion → net 1,825
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Difference: 85 a dayEighty-five calories a day, from the same number on the label. Over a year that is roughly 4 kg.
The calculator works this out for whatever split you enter, rather than leaving it as a fact about somebody else's diet.
But Keep It in Proportion
Eighty-five a day is real and it is small.
It is far smaller than the error in most calorie targets — the activity multiplier alone routinely moves a TDEE estimate by 300 calories. So the thermic effect is a reason to prefer protein at the margin, not a strategy that rescues a badly sized target.
Get the calorie figure roughly right first. Then let this nudge the split.
Fat Has a Floor, Carbohydrate Does Not
Below about 15% of calories from fat, the calculator flags it.
Fat is needed for hormone production and for absorbing vitamins A, D, E and K, so very low-fat splits carry costs the macro arithmetic cannot show you.
Carbohydrate has no equivalent minimum requirement — the body can make what glucose it needs. That does not make low-carb better, but it does mean carbohydrate is where there is genuine room to move if something has to give.
So the sensible order of operations is: set protein by bodyweight, keep fat above the floor, and let carbohydrate take whatever is left.
Precision Is Not the Point
These are targets to aim near, not hit.
Protein is the one worth being reasonably accurate about, because it has a requirement tied to your body. Carbohydrate and fat can shift between themselves week to week according to what you are training for and what you actually enjoy eating — and a split you enjoy is one you will still be following in three months, which matters more than any of the arithmetic here.
Understanding Your Result
Your macros gives all three in grams.
The split restates the percentages against your calories.
Protein per kilogram is the check that matters, with the percentage needed to fix a shortfall.
What digestion costs gives the thermic figure for your own split.
Worth knowing flags low fat, low protein, or puts the thermic effect in proportion.
When Should You Use This Calculator?
After setting calories. Macros are a second-order decision.
Especially in a deficit. That is when the protein check earns its place.
When cutting calories. The same split will have quietly dropped your protein.
To compare splits. The thermic figure makes the differences concrete.
Common Mistakes
Setting protein as a percentage. It scales with your body, not your calorie target.
Keeping the same split while cutting calories. Protein falls exactly when you need it most.
Chasing the thermic effect. It is worth 85 calories, not a plan.
Dropping fat below 15%. It has jobs the arithmetic does not show.
Treating the grams as exact. These are targets to aim near.
Optimising macros before calories. The larger number matters far more.
These are general guidelines and individual requirements vary with training, medical conditions and medication. Nothing here is medical or dietary advice — speak to a doctor or registered dietitian before making significant changes to what you eat.