BMR Calculator

Basal Metabolic Rate and TDEE: Mifflin-St Jeor Equation Calculations

Basal Metabolic Rate (BMR) represents the number of calories your body requires to maintain essential physiological functions while at complete rest. These functions include breathing, blood circulation, cell production, nutrient processing, protein synthesis, and maintaining body temperature. BMR accounts for approximately 60-75% of your total daily energy expenditure, making it the largest component of your calorie burn even before any physical activity.

Understanding your BMR and Total Daily Energy Expenditure (TDEE) is crucial for effective weight management, whether you are trying to lose fat, maintain weight, or build muscle. This calculator uses the scientifically validated Mifflin-St Jeor equation to provide accurate estimates. For comprehensive calorie planning, combine BMR calculations with your specific fitness goals and activity levels.

What is BMR (Basal Metabolic Rate)?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain vital functions like breathing, circulation, cell production, and temperature regulation. It represents 60-75% of your total daily calorie expenditure and is calculated using factors including age, gender, weight, and height. BMR is measured under strict laboratory conditions, while RMR (Resting Metabolic Rate) is measured under less restrictive conditions and is typically 10-20% higher.

Mifflin-St Jeor Formula for Men and Women

This calculator uses the Mifflin-St Jeor equation, developed in 1990 and considered the most accurate BMR formula for modern populations. The equations are:

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5

Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161

The formula accounts for the fact that men typically have higher muscle mass and lower body fat percentage than women, resulting in a higher baseline metabolic rate. The age factor reflects the natural decline in metabolism as we age, approximately 2% per decade after age 20.

Activity Level Multipliers: Sedentary to Extra Active

Your Total Daily Energy Expenditure (TDEE) is calculated by multiplying your BMR by an activity factor that represents your lifestyle:

• Sedentary (1.2): Little or no exercise, desk job
• Lightly Active (1.375): Light exercise 1-3 days per week
• Moderately Active (1.55): Moderate exercise 4-5 days per week
• Very Active (1.725): Hard exercise 6-7 days per week
• Extra Active (1.9): Very hard exercise daily, physical job or training twice per day

Calorie Deficit and Surplus for Weight Loss and Muscle Gain

Understanding your TDEE allows you to create effective calorie targets for your goals:

• Weight Loss: Create a 500-calorie daily deficit to lose approximately 1 pound per week
• Mild Weight Loss: Create a 250-calorie deficit for slower, more sustainable loss of 0.5 pounds per week
• Maintenance: Consume calories equal to your TDEE to maintain current weight
• Mild Weight Gain: Add 250 calories above TDEE for gradual muscle gain
• Weight Gain: Add 500 calories above TDEE for faster weight gain (ideal for bulking)

For targeted weight loss planning, combine your TDEE with realistic timelines and sustainable deficit strategies to achieve your goals safely.

Muscle Mass, Hormones, Sleep, and Metabolic Rate Factors

Several factors beyond the basic formula affect your metabolic rate:

• Muscle Mass: Muscle tissue burns more calories at rest than fat tissue, approximately 6 calories per pound daily
• Body Composition: Higher body fat percentage typically means lower BMR relative to body weight
• Genetics: Some people naturally have faster or slower metabolisms
• Hormones: Thyroid function, cortisol levels, and other hormones significantly impact metabolism
• Diet History: Chronic dieting can lower BMR through metabolic adaptation
• Sleep Quality: Poor sleep can reduce metabolic rate by 5-20%
• Stress Levels: Chronic stress affects hormone balance and metabolism

Strength Training, Protein, and Metabolism Optimization Strategies

While BMR is largely determined by factors you cannot control, you can optimize it:

• Build Muscle: Strength training increases muscle mass, raising your resting metabolic rate
• Stay Active: Regular exercise not only burns calories during activity but can elevate metabolism for hours afterward
• Eat Enough Protein: Protein has a higher thermic effect (20-30%) compared to carbs (5-10%) and fats (0-3%)
• Do Not Crash Diet: Severe calorie restriction can lower BMR by 10-15% through metabolic adaptation
• Stay Hydrated: Dehydration can slow metabolism; drinking cold water may temporarily boost it
• Get Quality Sleep: Aim for 7-9 hours nightly to maintain optimal metabolic function

For protein intake planning, use our protein calculator to determine optimal daily protein needs based on your weight and activity level.

BMR vs. RMR: What's the Difference?

BMR (Basal Metabolic Rate) is measured under strict laboratory conditions after 8 hours of sleep and 12 hours of fasting, in a darkened room at neutral temperature. RMR (Resting Metabolic Rate) is measured under less restrictive conditions and is typically 10-20% higher than BMR. For practical purposes, most calculators (including this one) estimate BMR, which provides a conservative baseline for calorie planning.

Calculator Accuracy and Individual Metabolic Variations

The Mifflin-St Jeor equation is accurate within 10% for most people, but individual variations exist. Athletes with high muscle mass may have higher BMRs than predicted, while those with metabolic conditions may have lower rates. For the most accurate measurement, consider professional metabolic testing using indirect calorimetry. However, this calculator provides an excellent starting point for most individuals planning their nutrition and fitness goals.

How Do I Calculate My BMR?

To calculate your BMR, use the Mifflin-St Jeor equation: For men, BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5. For women, BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161. Then multiply your BMR by your activity level (1.2 for sedentary to 1.9 for extra active) to get your TDEE, which represents your total daily calorie needs.

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