Athletes need more than a generic calorie number — they need fuel matched to the demands of their sport. This calculator applies ISSN per-kilogram guidelines to turn your bodyweight, training volume, and goal into concrete daily gram targets for each macronutrient.
How it works
Protein is set per kilogram of bodyweight by goal, and carbohydrate scales with weekly training hours:
protein = 1.4–2.2 g/kg (endurance → strength → cut)
carbs = 4 / 6 / 8 / 10 g/kg (by <5 / 5-10 / 10-15 / >15 h per week)
fat = remaining energy / 9 kcal/g, floored at 0.8 g/kgEnergy is estimated from bodyweight scaled by training load; a weight cut trims it by about 15 percent and drops carbohydrate one band to create a deficit while keeping protein high.
Why each macronutrient has its own logic
Protein is set per kilogram because muscle maintenance and growth depend primarily on absolute protein intake relative to lean mass, not on total calories. Higher protein needs during a cut (up to 2.2 g/kg) compensate for the reduced calorie availability and the body’s tendency to use protein for energy when total fuel is restricted.
Carbohydrate scales with training hours because carbohydrate is the primary fuel for moderate-to-hard intensity work. Muscle glycogen (stored carbohydrate) is the limiting factor in sessions above roughly 70–75% of VO2max. An endurance athlete doing 15+ hours per week has dramatically higher glycogen turnover than someone lifting for 4 hours — the carbohydrate band reflects this. Under-fuelling carbohydrate relative to training load leads to progressive glycogen depletion, reduced performance, and increased risk of muscle breakdown.
Fat fills the remaining energy after protein and carbohydrate are set. The floor of 0.8 g/kg protects sex hormone production, fat-soluble vitamin absorption, and joint health. Cutting fat below this floor to chase a calorie target impairs health markers and is not recommended.
Goal-specific guidance
Endurance athletes should prioritise carbohydrate timing: most carbohydrate in the hours before and after training sessions to pre-load and replenish glycogen. A large evening meal does not replenish glycogen as effectively as eating around the training window.
Strength athletes can tolerate lower relative carbohydrate but still benefit from carbohydrate around heavy sessions. The protein target is highest here (up to 2.2 g/kg) because muscle protein synthesis is the goal.
Weight cut. The tool reduces total calories by about 15% and drops carbohydrates one band, keeping protein at the high end. This is a moderate cut designed to preserve training quality. Very aggressive cuts below this level risk performance degradation and muscle loss even with high protein.
Worked example
A 75 kg strength athlete training 8 hours per week:
| Macronutrient | Amount | Calories |
|---|---|---|
| Protein | ~165 g | ~660 kcal |
| Carbohydrate | ~450 g (6 g/kg) | ~1,800 kcal |
| Fat | ~50–60 g (remainder, floored at 0.8 g/kg) | ~450–540 kcal |
| Total | — | ~2,910–3,000 kcal |
Distribute protein across 3–5 meals, time most carbohydrate around training sessions, and keep fat above the floor. Re-check numbers every 4 weeks as bodyweight changes, and treat performance and recovery quality as the real arbiter of whether your numbers are correct.