Energy balance dictates long-term body composition changes. The human body expends energy continuously to support basal cellular physiology, food digestion, and physical movement. Planning dietary changes requires establishing baseline maintenance requirements before introducing a caloric deficit for fat reduction or a caloric surplus for muscular hypertrophy.

### Tool Implementation and Calculation Logic The calculator executes the Mifflin-St Jeor equation, recognized in clinical nutrition reviews as one of the most reliable predictive formulas for healthy adults:

- **Basal Metabolic Rate (BMR):**\n - Men: $\text{BMR} = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) + 5$\n - Women: $\text{BMR} = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) - 161$\n- **Total Daily Energy Expenditure (TDEE):**\n - Sedentary: $\text{BMR} \times 1.2$\n - Light Exercise (1–3 days/week): $\text{BMR} \times 1.375$\n - Moderate Exercise (3–5 days/week): $\text{BMR} \times 1.55$\n - Heavy Exercise (6–7 days/week): $\text{BMR} \times 1.725$\n - Athlete: $\text{BMR} \times 1.9$\n- **Deficit and Surplus Targets:**\n - Maintenance: $\text{TDEE}$\n - Mild Fat Loss (-250 kcal/day): $\text{TDEE} - 250$\n - Standard Fat Loss (-500 kcal/day): $\text{TDEE} - 500$\n - Mild Muscle Gain (+300 kcal/day): $\text{TDEE} + 300$\n- **Maintenance Macronutrient Breakdown:**\n - Protein (30% of energy): $(\text{TDEE} \times 0.30) / 4\text{ kcal/g}$\n - Carbohydrates (40% of energy): $(\text{TDEE} \times 0.40) / 4\text{ kcal/g}$\n - Dietary Fats (30% of energy): $(\text{TDEE} \times 0.30) / 9\text{ kcal/g}$\n ### Worked Numeric Example Using the tool default settings for a 28-year-old male: - **Biological Sex:** Male - **Age:** 28 years - **Body Weight:** 75 kg - **Height:** 178 cm - **Activity Multiplier:** 1.375 (Light Exercise) - **BMR Calculation:** $(10 \times 75) + (6.25 \times 178) - (5 \times 28) + 5 = 750 + 1,112.5 - 140 + 5 = 1,727.5\text{ kcal/day}$ - **TDEE Calculation:** $1,727.5 \times 1.375 \approx 2,375\text{ kcal/day}$ - **Target Calorie Profiles:**\n - Weight Maintenance: 2,375 kcal/day - Mild Fat Loss (-0.5 lb/week): 2,125 kcal/day - Standard Fat Loss (-1.0 lb/week): 1,875 kcal/day - Mild Muscle Gain (+0.5 lb/week): 2,675 kcal/day - **Maintenance Macronutrient Targets:**\n - Protein: $(2,375 \times 0.30) / 4 = 178\text{ grams}$ - Carbohydrates: $(2,375 \times 0.40) / 4 = 238\text{ grams}$ - Healthy Fats: $(2,375 \times 0.30) / 9 = 79\text{ grams}$\n ### Educational Guidance and Local Execution Guarantee Nutritional needs vary with endocrine status, lean body mass percentage, and athletic demands. Caloric equations provide statistical approximations rather than absolute metabolic readings. Consult a registered dietitian or physician before embarking on aggressive caloric restrictions. All inputs and calculations process entirely client-side in your local web browser session. No personal biometrics, dietary goals, or body statistics are transmitted to external servers.