About

Muscle hypertrophy requires a sustained positive energy balance, known as a calorie surplus. This tool calculates the precise Total Daily Energy Expenditure (TDEE) and adds a strategic surplus to support tissue synthesis without excessive fat accumulation. Accuracy in this calculation prevents "spinning your wheels" (undereating) or gaining unnecessary adipose tissue (overeating).

The calculation utilizes the Mifflin-St Jeor equation, widely considered the most reliable for estimating Basal Metabolic Rate (BMR) in non-obese individuals. It adjusts for activity levels and allows users to distinguish between a conservative "Lean Bulk" approach and a more aggressive "Dirty Bulk." The output segments energy needs into macronutrients, as protein synthesis rates and glycogen replenishment are dependent on specific gram-per-pound ratios.

Formulas

The core estimation relies on the Mifflin-St Jeor equation for Basal Metabolic Rate (BMR), adjusted by an activity factor (A) and a surplus target (S).

Men: BMR = 10W + 6.25H − 5Age + 5

Women: BMR = 10W + 6.25H − 5Age − 161

Target: Calories = (BMR × A) + S

Where W is weight in kg, H is height in cm, and S ranges from 250 to 500 kcal depending on goals.

Reference Data

Activity Level	Multiplier	Description
Sedentary	1.2	Office job, little to no exercise
Lightly Active	1.375	Light exercise/sports 1-3 days/week
Moderately Active	1.55	Moderate exercise/sports 3-5 days/week
Very Active	1.725	Hard exercise/sports 6-7 days/week
Extra Active	1.9	Very hard exercise & physical job

Frequently Asked Questions

A Lean Bulk targets a surplus of 200-300 calories above maintenance, aiming to maximize muscle gain while minimizing fat gain. It requires strict tracking. A Dirty Bulk involves a surplus of 500+ calories, allowing for faster weight gain but typically resulting in significantly higher body fat accumulation.

Current sports nutrition consensus suggests 0.7 to 1.0 grams of protein per pound of body weight (1.6 to 2.2 g/kg) is sufficient to maximize muscle protein synthesis. Higher amounts provide diminishing returns.

The Activity Multiplier includes an estimate for NEAT based on general lifestyle descriptions. If you have a physically demanding job, select a higher activity tier regardless of your gym frequency.

Clinical studies have shown Mifflin-St Jeor to be more accurate than the older Harris-Benedict equation, with a narrower margin of error for modern populations.