Calculator Methodology
The formulas behind each calculator, written out so you can check the maths.
TDEE and maintenance calories
We estimate basal metabolic rate (BMR) with the Mifflin-St Jeor equation, then multiply by an activity factor to estimate total daily energy expenditure (TDEE).
| Men | BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 |
| Women | BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161 |
| Activity factors | Sedentary 1.2 · Light 1.375 · Moderate 1.55 · Very active 1.725 · Extra active 1.9 |
| TDEE page targets | Mild cut −200 · Aggressive cut −400 · Lean bulk +250 · Aggressive bulk +400 kcal/day |
Macros
The macros calculator starts from the same TDEE and applies a goal factor: × 1.12 to build muscle, × 1.00 to maintain and × 0.82 to lose fat. Protein is set at 2.0 g per kg of bodyweight (2.2 g/kg when losing fat) and fat at 1.0 g per kg. Carbohydrates fill the remaining calories at 4 kcal per gram. Protein and carbohydrates provide 4 kcal per gram and fat 9 kcal per gram.
BMI
BMI = weight (kg) ÷ height (m)². We use the standard adult categories: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese.
Unit conversions
Pounds are converted at about 2.205 lb per kilogram and feet-and-inches at 2.54 cm per inch. Switching units in a calculator converts your current values for you.
Limitations
- Equations estimate averages; individual energy expenditure varies by 10–15% or more.
- Activity level is the biggest source of error — most people overestimate it.
- The macros calculator displays at least 50 g of carbohydrate, which can nudge totals slightly above target at very low calories.
- BMI does not distinguish muscle from fat and is unreliable for athletes, older adults and under-18s.
- These tools are not medical advice. Use them as a starting point and adjust from real-world results.
Try them: TDEE calculator, macros calculator, BMI calculator.