How to use this Macro calculator
- Enter a daily energy target and body weight.
- Choose a protein assumption in grams per kilogram and a fat percentage.
- Select Calculate to see protein, carbohydrate and fat in grams.
The formula and method
Protein grams = body weight (kg) × your entered grams-per-kilogram assumption. The form accepts 0.8–2.5 g/kg/day and starts at 1.6; the default is an example rather than a personal prescription.
Fat grams = daily calories × fat percentage ÷ 100 ÷ 9. The form allows 20–40% and starts at 30%. Carbohydrate grams = (daily calories − protein grams × 4 − fat grams × 9) ÷ 4.
This arithmetic uses 4 kcal per gram for protein and carbohydrate and 9 kcal per gram for fat. If the entered protein and fat use more energy than the target provides, the tool reports an error instead of displaying negative carbohydrate.
Worked example
For an 80 kg lifter consuming 2,400 kcal/day with a 1.6 g/kg protein target and 30% fat: Protein = 80 × 1.6 = 128 g (512 kcal); Fat = (2,400 × 0.30) / 9 = 80 g (720 kcal); Carbs = (2,400 - 512 - 720) / 4 = 1,168 / 4 = 292 g (1,168 kcal).
Understanding the estimate
- The split is an arithmetic allocation, not a uniquely optimal diet or a meal plan.
- Food labels, fibre and food composition can make real dietary energy differ from a simple 4/4/9 calculation.
- This tool does not account for individual medical nutrition requirements.
Frequently asked questions
Why are carbohydrates the remainder?
The tool allocates protein and fat first, then assigns the remaining energy to carbohydrate. That is the chosen calculation order, not a claim that everyone needs that split.
Why did the tool reject my inputs?
A high protein assumption and fat allocation can exceed a low energy target. Change the assumptions or target so the arithmetic is possible.
Where should my calorie target come from?
The calorie and TDEE tools can show estimated scenarios. Use an appropriate target for your circumstances rather than assuming this macro split determines it.