Carb Calculator

What this calculator estimates

Estimate carbohydrate grams after allocating fixed protein and fat amounts within an estimated maintenance-energy intake. The form derives calories from body details; it does not accept a calorie target or custom macro split.

Inputs and calculation method

Enter age, equation option, height in cm, weight in kg and activity level. Maintenance energy is estimated using Mifflin–St Jeor × activity. The tool assumes protein of 1.7 g/kg and fat providing 28% of that energy, then assigns the remaining calories to carbohydrate.

Formula and units

Protein grams = weight × 1.7. Fat grams = maintenance kcal × 0.28 ÷ 9. Carbohydrate grams = (maintenance kcal − protein grams × 4 − fat grams × 9) ÷ 4. Displayed grams are rounded to whole numbers.

How to use it

1. Enter adult body details in years, cm and kg.
2. Choose the activity category closest to your usual week.
3. Calculate and read the assumed protein and fat alongside carbohydrate.
4. Use the macro calculator if you want its separate maintenance, loss or gain goal presets.

Worked example

For age 35, 165 cm, 70 kg, the female equation and Moderate activity (1.55), estimated maintenance is 2,162.64 kcal. Protein is 119 g and fat is about 67.28 g. Remaining carbohydrate is (2,162.64 − 476 − 605.54) ÷ 4 = 270.27 g, displayed as 270 g.

How to read the result

This is the remainder from one chosen set of presets, not an independently measured carbohydrate requirement. There is no training-goal, protein-target or fat-target control on this page.

Common mistakes

• Assuming the activity category measures actual daily expenditure.
• Reading the fixed 1.7 g/kg protein and 28% fat as personalised prescriptions.
• Adding these carbohydrates to a separate complete macro target.

Method limitations

The adult energy equation and fixed macro allocations cannot describe everyone’s appetite, sport or clinical needs. A very low or negative remainder indicates incompatible assumptions, not a recommendation to eat a negative amount of carbohydrate.

Sources and method references

• Mifflin–St Jeor original equation

Using the estimate

Read the carbohydrate result together with the two fixed allocations that produced it. It is one transparent planning scenario rather than a universal requirement.