Macro Nutrient Calculator

The Science of Macros

This calculator uses the Mifflin-St Jeor equation to estimate your Basal Metabolic Rate (BMR), which represents the calories your body burns at complete rest. It then multiplies this by an activity factor to get your Total Daily Energy Expenditure (TDEE). Mifflin-St Jeor is the equation most commonly recommended over the older Harris-Benedict formula because it tends to estimate resting metabolism more accurately for most adults.

Activity multiplier guide: 1.2 for sedentary (little to no exercise), 1.375 for lightly active (light exercise 1-3 days/week), 1.55 for moderately active (moderate exercise 3-5 days/week), 1.725 for very active (hard exercise 6-7 days/week), and 1.9 for extra active (physical job plus daily training).

Worked example. A 30-year-old male, 70 kg, 175 cm, at the "lightly active" multiplier (1.375), maintaining weight, gets a BMR of about 1,649 calories and a TDEE of about 2,267 calories/day. This splits into roughly 170 g protein, 227 g carbs, and 76 g fat under the 30/40/30 default. Choosing "Fat Loss" or "Muscle Gain" shifts the calorie target by 500 calories/day before that same split is applied.

Our default 30/40/30 split falls within the ranges recommended by the Dietary Guidelines for Americans, which set protein at 10-35%, fat at 20-35%, and carbohydrates at 45-65% of daily calories.

Limitations. BMR formulas are population averages and can be off by roughly 10% for any given individual. Highly muscular people are often underestimated, since the formula only inputs weight, height, age, and sex. These targets are a starting point, not medical advice; talk to a doctor or registered dietitian before making major changes, especially if you're pregnant, nursing, or managing a health condition.