BMR Calculator - Mifflin-St Jeor Equation

Calculate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) using the accurate Mifflin-St Jeor equation.

Determine your body's energy needs at rest and with different activity levels. The Mifflin-St Jeor equation is considered the most accurate BMR formula for healthy adults.

Examples

Click on any example to load it into the calculator.

Sedentary Office Worker

Sedentary

A 35-year-old male office worker with minimal physical activity.

Weight: 75 kg

Height: 180 cm

Age: 35 years

Gender: Male

Activity Level: Sedentary (little or no exercise)

Active Female Athlete

Active

A 25-year-old female athlete with regular intense exercise.

Weight: 60 kg

Height: 165 cm

Age: 25 years

Gender: Female

Activity Level: Very Active (hard exercise 6-7 days/week)

Moderately Active Adult

Moderate

A 40-year-old person with regular moderate exercise routine.

Weight: 70 kg

Height: 170 cm

Age: 40 years

Gender: Male

Activity Level: Moderate (moderate exercise 3-5 days/week)

Elderly Individual

Elderly

A 65-year-old person with light daily activities.

Weight: 65 kg

Height: 160 cm

Age: 65 years

Gender: Female

Activity Level: Lightly Active (light exercise 1-3 days/week)

Other Titles
Understanding BMR Calculator - Mifflin-St Jeor Equation: A Comprehensive Guide
Master the science of metabolism and energy expenditure using the most accurate BMR formula. Learn how to calculate, interpret, and apply BMR and TDEE values for optimal health and fitness outcomes.

What is the Mifflin-St Jeor BMR Calculator?

  • Core Concepts and Definitions
  • Why the Mifflin-St Jeor Equation is Superior
  • The Science Behind BMR
The Mifflin-St Jeor BMR Calculator is a scientifically validated tool that estimates your Basal Metabolic Rate (BMR)—the number of calories your body burns at complete rest to maintain basic life functions like breathing, circulation, cell production, nutrient processing, protein synthesis, and ion transport. This calculator uses the Mifflin-St Jeor equation, which is considered the most accurate BMR formula for healthy adults, developed in 1990 and validated across diverse populations.
The Superiority of Mifflin-St Jeor Equation
The Mifflin-St Jeor equation is preferred over other BMR formulas (like Harris-Benedict) because it was developed using more modern measurement techniques and provides more accurate estimates for contemporary populations. Research has shown that the Mifflin-St Jeor equation predicts BMR with an accuracy of ±10% compared to measured values, making it the gold standard for BMR calculation in healthy adults. The equation specifically accounts for the four primary factors that influence BMR: body weight, height, age, and gender.
The Mathematical Precision of Mifflin-St Jeor
The Mifflin-St Jeor equation uses different coefficients for males and females, reflecting the biological differences in body composition and metabolic rates between genders. For men: BMR = (10 × weight) + (6.25 × height) - (5 × age) + 5. For women: BMR = (10 × weight) + (6.25 × height) - (5 × age) - 161. These formulas have been extensively validated and provide estimates within 10% of measured BMR values, making them suitable for clinical and personal use applications.
Beyond BMR: Total Daily Energy Expenditure
While BMR represents your body's energy needs at rest, Total Daily Energy Expenditure (TDEE) accounts for all your daily activities. TDEE is calculated by multiplying your BMR by an activity factor that ranges from 1.2 (sedentary) to 1.9 (extremely active). This comprehensive approach ensures that your calorie calculations reflect your actual lifestyle and energy needs, providing a more accurate foundation for nutrition planning and weight management strategies.

Key Concepts Explained:

  • BMR: Calories burned at complete rest for basic life functions
  • TDEE: Total daily calories including all activities and exercise
  • Activity Factors: Multipliers that account for different activity levels
  • Energy Balance: The relationship between calories consumed and expended

Step-by-Step Guide to Using the BMR Calculator

  • Data Collection and Preparation
  • Input Methodology
  • Result Interpretation and Application
Accurate BMR calculation requires precise data collection and thoughtful interpretation. Follow this systematic approach to ensure your results provide a reliable foundation for your nutrition and fitness planning.
1. Accurate Body Measurements
Begin with precise weight and height measurements. Weigh yourself in the morning, after using the bathroom but before eating, wearing minimal clothing. Use a reliable scale and measure your height without shoes, standing straight against a wall. These measurements should be as current as possible, as even small changes can affect your BMR calculation. For the most accurate results, take multiple measurements over several days and use the average values.
2. Age and Gender Considerations
Enter your current age in years—the Mifflin-St Jeor equation accounts for the natural decline in metabolism that occurs with aging. Select your biological gender, as the equation uses different coefficients for males and females. These differences reflect variations in body composition, with males typically having higher muscle mass and lower body fat percentages, leading to higher metabolic rates.
3. Activity Level Assessment
Honestly assess your typical daily activity level. Sedentary includes desk jobs with little exercise, lightly active includes light exercise 1-3 days per week, moderate includes moderate exercise 3-5 days per week, very active includes hard exercise 6-7 days per week, and extremely active includes very hard exercise and physical job. Be realistic about your activity level, as overestimating can lead to consuming more calories than you actually need.
4. Interpreting and Applying Results
Your BMR represents your baseline calorie needs at rest. Your TDEE represents your total daily calorie needs including all activities. For weight maintenance, consume calories equal to your TDEE. For weight loss, create a deficit of 500-1000 calories per day (aiming for 0.5-1 kg per week). For weight gain, create a surplus of 300-500 calories per day. Remember that these are estimates, and individual variations may require adjustments based on your progress and goals.

Activity Level Guidelines:

  • Sedentary (1.2): Desk job, little exercise
  • Lightly Active (1.375): Light exercise 1-3 days/week
  • Moderate (1.55): Moderate exercise 3-5 days/week
  • Very Active (1.725): Hard exercise 6-7 days/week
  • Extremely Active (1.9): Very hard exercise, physical job

Real-World Applications and Health Implications

  • Weight Management Strategies
  • Nutrition Planning
  • Fitness and Athletic Performance
The Mifflin-St Jeor BMR Calculator serves as a powerful tool for various health and fitness applications, from basic weight management to advanced athletic performance optimization.
Weight Loss and Management
For weight loss, understanding your BMR and TDEE is essential for creating an effective calorie deficit. A deficit of 500 calories per day typically results in 0.5 kg of weight loss per week, while a 1000-calorie deficit results in 1 kg per week. However, it's important not to create too large a deficit, as consuming fewer calories than your BMR can slow your metabolism and lead to muscle loss. The calculator helps you find the sweet spot between effective weight loss and maintaining metabolic health.
Muscle Building and Athletic Performance
For muscle building, you need to consume more calories than your TDEE to provide the energy and nutrients needed for muscle growth. A surplus of 300-500 calories per day is typically sufficient for muscle gain while minimizing fat accumulation. Athletes and bodybuilders often use BMR calculations as the foundation for more complex nutrition plans that include specific macronutrient ratios, meal timing, and supplementation strategies.
Medical and Clinical Applications
Healthcare professionals use BMR calculations to develop nutrition plans for patients with various medical conditions, including diabetes, heart disease, and eating disorders. The Mifflin-St Jeor equation is particularly useful in clinical settings because it provides reliable estimates without requiring expensive equipment or invasive procedures. It's also used in research studies to standardize energy requirements across different populations and conditions.

Practical Applications:

  • Weight Loss: Create 500-1000 calorie daily deficit
  • Muscle Gain: Create 300-500 calorie daily surplus
  • Maintenance: Match calorie intake to TDEE
  • Medical Nutrition: Base clinical nutrition plans on BMR

Common Misconceptions and Correct Methods

  • Myths About Metabolism
  • Accurate Calculation Methods
  • Individual Variations
Understanding BMR and metabolism involves dispelling common myths and recognizing the factors that truly influence energy expenditure. This knowledge helps you make informed decisions about your nutrition and fitness strategies.
Metabolism Myths and Realities
One common myth is that eating certain foods can significantly boost your metabolism. While some foods may have a small thermic effect, the impact is minimal compared to your overall BMR. Another myth is that metabolism slows dramatically with age—while there is some decline, it's primarily due to loss of muscle mass rather than age itself. Regular strength training can help maintain muscle mass and metabolic rate as you age.
Factors That Actually Affect BMR
The primary factors affecting BMR are body composition (muscle mass vs. fat mass), age, gender, and body size. Muscle tissue is metabolically active and burns more calories at rest than fat tissue. This is why strength training is important for maintaining a healthy metabolism. Other factors include genetics, hormonal status, and environmental temperature, but these have smaller effects compared to the main factors.
Individual Variations and Adjustments
While the Mifflin-St Jeor equation provides accurate estimates for most people, individual variations exist. Some people may have higher or lower BMR than predicted due to genetic factors, medical conditions, or medications. It's important to monitor your progress and adjust your calorie intake based on actual results rather than relying solely on calculated values. Regular reassessment of your BMR and TDEE is recommended, especially after significant weight changes.

Common Misconceptions:

  • Myth: Eating spicy food significantly boosts metabolism
  • Myth: Metabolism dramatically slows with age
  • Reality: Muscle mass is the primary factor affecting BMR
  • Reality: Individual variations exist and require monitoring

Mathematical Derivation and Examples

  • The Mifflin-St Jeor Formula
  • Calculation Examples
  • Activity Factor Multipliers
Understanding the mathematical foundation of the Mifflin-St Jeor equation helps you appreciate its accuracy and apply it effectively in various scenarios.
The Mifflin-St Jeor Formula Derivation
The Mifflin-St Jeor equation was developed by analyzing data from healthy adults using indirect calorimetry, the gold standard for measuring energy expenditure. The formula accounts for the fact that larger bodies require more energy (weight and height terms), that metabolism decreases with age (negative age term), and that males typically have higher metabolic rates than females (different constants). The equation provides a linear relationship that accurately predicts BMR across a wide range of body sizes and ages.
Calculation Examples
For a 30-year-old male weighing 75 kg and 180 cm tall: BMR = (10 × 75) + (6.25 × 180) - (5 × 30) + 5 = 750 + 1125 - 150 + 5 = 1730 calories/day. For a 25-year-old female weighing 60 kg and 165 cm tall: BMR = (10 × 60) + (6.25 × 165) - (5 × 25) - 161 = 600 + 1031.25 - 125 - 161 = 1345.25 calories/day. These examples show how the equation accounts for gender differences and body size variations.
Activity Factor Calculations
Activity factors are multipliers that convert BMR to TDEE. For the male example above with moderate activity: TDEE = 1730 × 1.55 = 2681.5 calories/day. For weight loss, subtract 500 calories: 2681.5 - 500 = 2181.5 calories/day. For weight gain, add 300 calories: 2681.5 + 300 = 2981.5 calories/day. These calculations provide practical targets for different fitness goals.

Mathematical Examples:

  • Male BMR: (10 × weight) + (6.25 × height) - (5 × age) + 5
  • Female BMR: (10 × weight) + (6.25 × height) - (5 × age) - 161
  • TDEE: BMR × Activity Factor
  • Weight Loss: TDEE - 500 calories