Table of Contents

📐 Formulas & Science

Mifflin-St Jeor Equation (BMR)

For Men:

$$BMR = 10 \times \text{weight(kg)} + 6.25 \times \text{height(cm)} - 5 \times \text{age} + 5$$

For Women:

$$BMR = 10 \times \text{weight(kg)} + 6.25 \times \text{height(cm)} - 5 \times \text{age} - 161$$

Total Daily Energy Expenditure (TDEE)

$$TDEE = BMR \times \text{Activity Factor}$$
Activity Factors:
  • Sedentary: 1.2 (desk job, no exercise)
  • Lightly Active: 1.375 (light exercise 1-3 days/week)
  • Moderately Active: 1.55 (moderate exercise 3-5 days/week)
  • Very Active: 1.725 (hard exercise 6-7 days/week)
  • Extremely Active: 1.9 (physical job + daily exercise)

Thermic Effect of Food (TEF)

TEF accounts for 10-15% of total daily energy expenditure:

  • Protein: 20-35% of calories used in digestion
  • Carbohydrates: 5-15% of calories used in digestion
  • Fats: 0-5% of calories used in digestion

Weight Change Calculations

Weight Loss:
$$\text{Target Calories} = TDEE - \text{Deficit}$$
500 cal deficit ≈ 0.5kg/week loss
Weight Gain:
$$\text{Target Calories} = TDEE + \text{Surplus}$$
500 cal surplus ≈ 0.5kg/week gain

📋 How to Use This Calculator

Step-by-Step Guide

  1. Enter Personal Info: Age, gender (affects BMR significantly)
  2. Input Body Measurements: Weight and height in your preferred units
  3. Select Activity Level: Be honest about your typical weekly activity
  4. Choose Your Goal: Weight loss, maintenance, or gain
  5. Review Results: BMR, TDEE, target calories, and macros

💡 Pro Tips

  • • Start conservatively with activity level
  • • Track for 2-3 weeks and adjust if needed
  • • Aim for 0.5-1kg weight change per week maximum
  • • Consider body composition, not just weight
  • • Consult professionals for medical conditions

📊 Real Examples

Example 1: Active Female

Profile: 28-year-old woman, 65kg, 165cm, moderately active
BMR: 10×65 + 6.25×165 - 5×28 - 161 = 1,444 calories
TDEE: 1,444 × 1.55 = 2,238 calories
For 0.5kg loss/week: 2,238 - 500 = 1,738 calories

Example 2: Sedentary Male

Profile: 35-year-old man, 80kg, 180cm, sedentary
BMR: 10×80 + 6.25×180 - 5×35 + 5 = 1,805 calories
TDEE: 1,805 × 1.2 = 2,166 calories
For maintenance: 2,166 calories

🔍 Understanding Your Results

BMR (Basal Metabolic Rate)

Calories your body needs at complete rest for basic functions like breathing, circulation, and cellular repair.

TDEE (Total Daily Energy)

Your maintenance calories - eat this amount to maintain current weight while accounting for daily activities.

Target Calories

Adjusted calories for your specific goal - deficit for loss, surplus for gain, maintenance for stability.

Macronutrient Distribution

Protein (25%): Essential for muscle maintenance, satiety, and metabolic function. Higher protein supports muscle preservation during weight loss.
Carbohydrates (45%): Primary energy source for brain and muscles. Focus on complex carbs for sustained energy.
Fats (30%): Necessary for hormone production, nutrient absorption, and cellular function. Include healthy fats like nuts, oils, and fish.

❓ Frequently Asked Questions

How accurate is the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation is considered the most accurate predictive equation for BMR in healthy adults, with about 90% accuracy. It's more precise than the older Harris-Benedict equation and is recommended by nutrition professionals.

Why is my BMR different from online calculators?

Different calculators use different equations (Harris-Benedict, Katch-McArdle, etc.). Our calculator uses the most current and accurate Mifflin-St Jeor equation, which may give slightly different results than older formulas.

Should I eat below my BMR for weight loss?

Generally no. Eating significantly below BMR can slow metabolism, cause muscle loss, and lead to nutrient deficiencies. Aim for a moderate deficit from your TDEE instead (300-500 calories below maintenance).

How often should I recalculate my calorie needs?

Recalculate every 10-15 pounds of weight change, when your activity level changes significantly, or every 2-3 months. Your calorie needs decrease as you lose weight and increase as you gain muscle mass.

How do medications affect calorie calculations?

Certain medications, particularly those affecting metabolism (like thyroid medications, steroids, or antidepressants), can influence your calorie needs. Monitor your weight and energy levels when starting new medications and adjust your calorie intake accordingly.

How does muscle mass affect calorie needs?

Muscle tissue is metabolically active and burns more calories than fat tissue. People with higher muscle mass typically need more calories than the calculator suggests. Consider adding 10-15% to your calculated needs if you have above-average muscle mass.

🎯 Applications & Use Cases

Personal Health & Fitness

  • ✓ Weight management planning
  • ✓ Meal planning and prep
  • ✓ Fitness goal setting
  • ✓ Understanding metabolism
  • ✓ Tracking progress over time

Professional & Educational

  • • Nutrition counseling
  • • Personal training programs
  • • Health education classes
  • • Sports nutrition planning
  • • Research and case studies

⚠️ Limitations & Considerations

Important Limitations

  • ⚠
    Individual Variation: Metabolic rates can vary ±10-15% between individuals due to genetics, medical conditions, and body composition.
  • ⚠
    Activity Estimation: Activity factors are averages; your actual activity may differ from standard categories.
  • ⚠
    Medical Conditions: Thyroid disorders, medications, and metabolic conditions can significantly affect calorie needs.
  • ⚠
    Body Composition: Muscle tissue burns more calories than fat tissue; athletes may need higher calories than predicted.

⚡ When to Consult Professionals

  • • Eating disorders or disordered eating patterns
  • • Significant medical conditions (diabetes, heart disease, etc.)
  • • Pregnancy or breastfeeding
  • • Under 18 or over 65 years old
  • • Taking medications that affect metabolism
  • • Competitive athletes or extreme training

📚 Scientific References

1. Mifflin MD, et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 51(2), 241-247.

2. American College of Sports Medicine. (2021). Guidelines for Exercise Testing and Prescription, 11th Edition.

3. Academy of Nutrition and Dietetics. (2023). Position Stand on Weight Management.