Macro split calculator: convert daily calories and your goal into protein, carb, and fat gram targets for cutting, maintaining, or bulking. Free, no signup.
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These tools provide general estimates for planning and education only.
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A Worked Example: 2,000 Calories, 150 g Protein, 60 g Fat
Start with a 2,000 kcal target and fixed 150 g protein and 60 g fat. Protein contributes 150 x 4 = 600 kcal and fat contributes 60 x 9 = 540 kcal, so 1,140 kcal are locked in. That leaves 2,000 - 1,140 = 860 kcal for carbohydrate, and since carbs also carry 4 kcal per gram, the carb allotment is 860 / 4 = 215 g.
Expressed as percentages of the calorie budget, protein is 600 / 2,000 = 30%, fat is 540 / 2,000 = 27%, and carbohydrate is 860 / 2,000 = 43%. The formula returns exactly these values: it always allocates protein and fat first, then treats carbs as the flexible remainder. That ordering matters in practice. If you raise protein to 200 g, carbs drop to 2000 - (800 + 540) all divided by 4, which is 165 g; the split shifts but the calorie total never changes. Every gram of protein or fat you add displaces roughly 1.35 g (protein) or 2.25 g (fat) of carbohydrate.
When the Split Becomes Physically Tight
The formula flags an error whenever protein and fat calories alone exceed the target, because negative grams of carbohydrate are impossible. A 1,500 kcal target with 180 g protein (720 kcal) and 90 g fat (810 kcal) sums to 1,530 kcal and fails immediately. The same macro grams fit easily in a 2,200 kcal target, leaving 220 g of carbs, so the error is about the target, not the macros themselves.
A subtler edge case is a technically valid but nearly carb-free split. On 1,500 kcal with 180 g protein and 80 g fat, carbs come out to just 15 g (720 + 720 = 1,440 kcal used, 4% of the budget). That is a ketogenic-leaning prescription, and whether it is sensible depends on training volume and preference. Practical benchmarks: active adults typically land between 2 and 5 g of carbs per kg of body weight daily, so a 70 kg runner at 15 g carbs per day would be far below what sustained hard sessions demand. Treat very low carb outputs as a prompt to either raise calories or trim protein and fat, not as a prescription.
