How the calculation works
First the calculator estimates your daily calories with the Mifflin-St Jeor equation and your activity level, the same way as the calorie calculator, and adds or subtracts the amount for your goal. Then it divides those calories over the three nutrients.
Protein (g) = body weight (kg) × grams per kg
Fat (g) = calories × fat share ÷ 9
Carbohydrate (g) = (calories − protein × 4 − fat × 9) ÷ 4
Protein and carbohydrate give 4 calories per gram, fat gives 9. Carbohydrate is never shown below 0.Worked example
65 kg, 2,085 calories a day, balanced split.
- Protein: 65 × 1.2 = 78 g, which is 312 calories.
- Fat: 2,085 × 0.30 ÷ 9 = 69.5 g, which is 625.5 calories.
- Carbohydrate: (2,085 − 312 − 625.5) ÷ 4 = 286.9 g.
What this calculator does not include
- Fibre, sugar, alcohol and the quality of your food.
- Special diets, sports plans and medical conditions.
- Real needs, which differ from person to person. Treat the grams as a starting point and adjust to how you feel and how your weight changes.
Results are estimates for information, not medical advice. Last updated: 12 November 2026.
Frequently asked questions
What are macros?
Macros, short for macronutrients, are protein, fat and carbohydrate. They are the three nutrients that give you calories, apart from alcohol. Protein and carbohydrate give 4 calories per gram and fat gives 9.
How are my macros worked out here?
The calculator first works out your daily calorie goal. Then it sets protein per kilogram of body weight, gives fat a share of the calories, and lets carbohydrate fill the rest.
How much protein do I need?
It depends on your size, goal and training. The splits here use 1.2, 1.6 or 1.8 grams per kilogram of body weight as common starting points. If you have a kidney condition or any health concern, ask a doctor or dietitian first.
Is this suitable for everyone?
No. It is for healthy adults aged 18 and over. It does not fit children, pregnancy, breastfeeding, medical conditions or a history of eating problems. Ask a doctor or dietitian for advice that fits you.