This calculator applies user-specified percentage splits to your Total Daily Energy Expenditure (TDEE) and converts those calorie allocations into grams of protein, carbohydrates, and fat. It does not recommend a particular split—it simply performs the arithmetic to show how many grams of each macronutrient correspond to your chosen percentages.

How Macro Split Calculator works

You provide three values: your TDEE in kilocalories, the percentage of calories you want from protein, and the percentage from carbohydrates. The tool automatically calculates fat as the remainder (100 - protein% - carbs%). It then divides protein and carbohydrate calories by 4 (since both yield 4 kcal/g) and fat calories by 9 (fat yields 9 kcal/g) to produce gram targets. The result is displayed as a P / C / F gram breakdown alongside calorie subtotals.

The formula

For each macronutrient:
• Protein grams = (TDEE × protein%) ÷ 100 ÷ 4
• Carbs grams = (TDEE × carbs%) ÷ 100 ÷ 4
• Fat grams = (TDEE × [100 - protein% - carbs%]) ÷ 100 ÷ 9

The constants 4 and 9 represent the Atwater general factors: carbohydrate and protein each supply approximately 4 kilocalories per gram, while fat supplies approximately 9 kilocalories per gram. These coefficients are used globally in nutrition labeling and were established through bomb-calorimetry studies in the late 19th and early 20th centuries.

Where this method is most accurate

This tool performs unit conversion—it does not estimate TDEE or recommend macro ratios. Accuracy depends entirely on the accuracy of the TDEE figure entered. The Atwater factors are general averages; the true metabolizable energy from protein, for example, ranges from 3.2 to 4.3 kcal/g depending on amino-acid profile and individual digestive efficiency. Mixed-diet populations see good agreement with the 4/4/9 model, but very high-fiber or high-resistant-starch diets may yield slightly lower realized energy.

What this tool does not do

It does not calculate or estimate your TDEE—that figure must come from a separate tool or method. It does not prescribe optimal macronutrient ranges for any goal, condition, or training phase. It does not account for meal timing, fiber, micronutrients, or the thermic effect of food. The output is a purely arithmetic conversion; it carries no recommendation about whether a given split is suitable or effective.

Disclaimer

This calculator is an educational tool that performs arithmetic conversions. It is not medical, nutritional, or training advice and does not diagnose, treat, or prevent any condition. Consult a registered dietitian or physician before making changes to your diet, especially if you have metabolic disorders, food allergies, or other health concerns.