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Mifflin-St Jeor BMR Calculator

Calculate your Basal Metabolic Rate (BMR) - the number of calories your body needs at complete rest to maintain vital functions.

Personal Information

How to Use This Calculator

Follow these steps for accurate BMR results:

  1. Select your preferred unit system (metric or imperial)
  2. Enter your gender, as BMR calculations differ between males and females
  3. Input your height, weight, and age
  4. Select your activity level to calculate TDEE (Total Daily Energy Expenditure)
  5. Click "Calculate BMR & TDEE" to view your results

Your BMR represents the calories your body needs at complete rest. Your TDEE factors in your activity level to show total calories needed daily.

The Mifflin-St Jeor Equation:

For men: BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age(y) + 5 For women: BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age(y) - 161

For the most accurate results, take measurements in the morning before eating and wearing minimal clothing.

Your Basal Metabolic Rate (BMR)

1,627
Calories/day

This is the number of calories your body requires at complete rest to maintain vital functions like breathing, circulation, and cell production. Your BMR is based on your gender, age, height, and weight.

Your Total Daily Energy Expenditure (TDEE)

2,522
Calories/day

Your TDEE represents the total calories you burn in a day when factoring in your activity level. This is calculated by multiplying your BMR by an activity factor of 1.55.

TDEE Breakdown By Activity Level

Activity Level Description TDEE (Calories/day)
Sedentary Little or no exercise 1,953
Lightly Active Light exercise/sports 1-3 days/week 2,237
Moderately Active Moderate exercise/sports 3-5 days/week 2,522
Very Active Hard exercise/sports 6-7 days a week 2,807
Extra Active Very hard exercise, physical job or training twice a day 3,092

What To Do With Your Results

Now that you know your BMR and TDEE, here's how you can use this information:

For Weight Maintenance:

Consume approximately the same number of calories as your TDEE to maintain your current weight.

For Weight Loss:
  • Moderate weight loss: Consume 300-500 calories less than your TDEE
  • This creates a deficit that should result in losing about 0.5-1 pound per week
  • Do not consume fewer calories than your BMR without medical supervision
For Weight Gain:
  • Consume 300-500 calories more than your TDEE
  • For building muscle, combine with appropriate strength training
  • Focus on nutritious foods for healthy weight gain

Remember that these calculations provide estimates. Individual metabolism can vary based on factors not accounted for in this calculator. For personalized nutrition advice, consult with a healthcare professional or registered dietitian.

What is BMR?
About the Formula
Factors Affecting BMR
Comparison to Other Formulas

What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR) represents the minimum amount of energy (calories) your body requires to perform essential functions while at complete rest. These functions include:

  • Breathing and circulation
  • Brain and nervous system function
  • Cell production and regeneration
  • Protein synthesis
  • Maintaining body temperature
  • Ion transport across cell membranes

BMR typically accounts for 60-75% of your total daily energy expenditure, making it the largest component of your calorie needs. The remaining calories are used for physical activity and the thermic effect of food (energy used to digest food).

Understanding your BMR is crucial for effective weight management, as it serves as the baseline for determining how many calories you need to consume based on your goals (weight maintenance, loss, or gain).

It's important to note that BMR differs from Resting Metabolic Rate (RMR), though the terms are often used interchangeably. BMR is measured under more strict conditions after at least 8 hours of sleep and 12 hours of fasting, while RMR can be measured under less restrictive conditions.

About the Mifflin-St Jeor Formula

The Mifflin-St Jeor equation was published in 1990 by Dr. Mark D. Mifflin, Dr. Sachiko T. St. Jeor, and their colleagues. It has since become one of the most widely respected and accurate methods for estimating BMR.

This equation calculates BMR based on weight, height, age, and gender, and is expressed as follows:

For men: BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age(years) + 5 For women: BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age(years) - 161

Research has demonstrated that the Mifflin-St Jeor equation tends to be more accurate than older formulas (like Harris-Benedict or Owen) for most individuals, particularly in modern populations. A 2005 review in the Journal of the American Dietetic Association found it to be the most accurate predictive equation for estimating BMR in non-obese and obese adults.

While the formula is considered highly reliable for the general population, it may be less accurate for individuals who are very muscular, extremely lean, or those with certain medical conditions that affect metabolism. In these cases, more direct methods of measuring energy expenditure may be recommended.

Factors Affecting Your BMR

Your basal metabolic rate is influenced by numerous factors, many of which are not accounted for in standard predictive equations:

  • Body Composition: Muscle tissue is more metabolically active than fat tissue. Individuals with higher muscle mass typically have higher BMRs than those with similar weight but higher body fat percentage.
  • Age: BMR typically decreases with age, primarily due to loss of muscle mass and hormonal changes. This decline is often estimated at about 2-3% per decade after age 20.
  • Genetics: Family history plays a significant role in determining your baseline metabolism. Some people naturally have faster or slower metabolic rates.
  • Hormonal Factors: Thyroid hormones particularly influence BMR. Conditions like hypothyroidism can slow metabolism, while hyperthyroidism can increase it.
  • Gender: Men generally have higher BMRs than women due to greater muscle mass and lower body fat percentages.
  • Environmental Temperature: Exposure to extreme cold can temporarily increase BMR as the body works to maintain core temperature.
  • Pregnancy and Lactation: Women's BMR increases during pregnancy and while breastfeeding to support the needs of the developing baby or milk production.
  • Fever and Illness: BMR increases during fever (approximately 7% for each degree Fahrenheit increase) and during recovery from illness or injury.
  • Nutritional Status: Severe caloric restriction can decrease BMR as the body adapts to conserve energy, while overfeeding can temporarily increase it.

Understanding these factors helps explain why two people of the same height, weight, age, and gender might have different caloric needs for weight maintenance.

Comparison to Other BMR Formulas

Several equations exist for estimating BMR, each with their own strengths and limitations:

  • Harris-Benedict Equation (1919): One of the oldest and most widely used formulas. While still used today, it was developed based on a small sample of predominantly young, fit individuals and tends to overestimate BMR in many modern populations.
  • Revised Harris-Benedict Equation (1984): An updated version that improved accuracy somewhat but still shows similar limitations as the original.
  • Mifflin-St Jeor Equation (1990): Generally considered the most accurate for healthy adults in the general population. Research shows it provides estimates within 10% of measured BMR for about 82% of individuals.
  • Owen Equation (1986/1987): Developed from studies on relatively small samples, this equation often underestimates BMR, especially in more active individuals.
  • Katch-McArdle Formula: Unique in that it accounts for lean body mass instead of total weight, potentially making it more accurate for athletes and those with significantly different body compositions than average. However, it requires knowing your body fat percentage.
  • WHO/FAO/UNU Equations: Developed by international health organizations, these equations provide different formulas for different age ranges but may not be as accurate as Mifflin-St Jeor for most adults.

A 2005 review published in the Journal of the American Dietetic Association evaluated these equations and concluded that the Mifflin-St Jeor formula was the most accurate, with the lowest error rates compared to actual measured BMR in most populations.

For most healthy adults, the Mifflin-St Jeor equation provides a reasonable estimate of BMR that can serve as a starting point for nutritional planning. However, individual results may vary, and adjustments based on personal response are often necessary.

Picture of Dr. Evelyn Carter

Dr. Evelyn Carter

Author | Chief Calculations Architect & Multi-Disciplinary Analyst

Table of Contents

Mifflin-St Jeor BMR Calculator: The Most Accurate Way to Determine Your Daily Caloric Needs

Understanding your body’s energy requirements is essential for effective weight management, fitness planning, and overall health. Our comprehensive Mifflin-St Jeor BMR calculator above helps you determine your Basal Metabolic Rate and Total Daily Energy Expenditure with scientific precision, providing personalized insights based on your unique physical characteristics.

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Understanding Basal Metabolic Rate: The Foundation of Your Energy Needs

Your Basal Metabolic Rate (BMR) represents the minimum amount of energy your body requires at complete rest to maintain vital functions. This includes everything from breathing and blood circulation to cell production and brain function. BMR typically accounts for 60-75% of your total daily calorie expenditure, making it the most significant factor in determining your energy needs.

Why BMR Matters for Health and Fitness

  • Weight management – Knowing your BMR provides the baseline for creating effective calorie targets
  • Preventing metabolic damage – Helps ensure you don’t restrict calories too severely
  • Exercise planning – Allows for more precise calculation of calorie deficits or surpluses
  • Personalized nutrition – Enables tailored meal planning based on your specific needs
  • Metabolic health tracking – Provides a benchmark to monitor changes in metabolism over time

While various formulas exist for estimating BMR, the Mifflin-St Jeor equation has emerged as the gold standard in nutritional science. Research has consistently shown it to be more accurate than older formulas like Harris-Benedict, particularly for diverse modern populations.

The Science Behind the Mifflin-St Jeor Equation

Developed in 1990 by researchers Dr. Mark D. Mifflin and Dr. Sachiko T. St. Jeor, this equation calculates BMR based on gender, weight, height, and age. The formula accounts for the metabolic differences between men and women and adjusts for the natural decline in metabolism that occurs with aging.

The Formula Explained

The Mifflin-St Jeor equation uses the following formulas:

  • For men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
  • For women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161

These specific coefficients were derived from extensive research and have been validated across multiple studies with diverse populations. The formula considers that men generally have higher metabolic rates due to greater muscle mass, and that metabolism naturally decreases with age.

Research Validation

The Mifflin-St Jeor equation has been extensively validated in research studies:

  • A 2005 review in the Journal of the American Dietetic Association found it to be the most accurate predictive equation for estimating BMR, with the lowest error rate compared to directly measured energy expenditure
  • Multiple studies have confirmed its applicability across different ethnicities, age groups, and body compositions
  • The equation provides estimates within 10% of measured BMR for approximately 82% of healthy adults
  • It performs consistently well across normal, overweight, and obese individuals

This scientific validation explains why the Mifflin-St Jeor equation has become the preferred method for estimating BMR in clinical and fitness settings.

Understanding Your Total Daily Energy Expenditure (TDEE)

While BMR represents your body’s energy needs at complete rest, Total Daily Energy Expenditure (TDEE) accounts for all the calories you burn throughout the day, including physical activity. Our calculator determines your TDEE by multiplying your BMR by an activity factor based on your typical activity level.

Sedentary (Activity Factor: 1.2)

Description: Little or no exercise, desk job

Example activities: Office work, driving, watching TV, reading, typing, light housework

Calculation: BMR × 1.2

Lightly Active (Activity Factor: 1.375)

Description: Light exercise 1-3 days per week

Example activities: Walking, light gardening, casual cycling, yoga, light weight training

Calculation: BMR × 1.375

Moderately Active (Activity Factor: 1.55)

Description: Moderate exercise 3-5 days per week

Example activities: Jogging, moderate cycling, recreational sports, moderate weight training, dancing

Calculation: BMR × 1.55

Very Active (Activity Factor: 1.725)

Description: Hard exercise 6-7 days per week

Example activities: Running, intense cycling, team sports, heavy weight training, HIIT workouts

Calculation: BMR × 1.725

Extra Active (Activity Factor: 1.9)

Description: Very hard daily exercise or physical job

Example activities: Professional athletes, construction workers, farm workers, twice-daily training sessions

Calculation: BMR × 1.9

Understanding both your BMR and TDEE provides a complete picture of your body’s energy requirements and creates a solid foundation for making informed decisions about nutrition and exercise.

Using Your BMR and TDEE for Health and Fitness Goals

Once you’ve calculated your BMR and TDEE using our calculator, you can apply this information to support various health and fitness objectives:

Weight Maintenance

  • Calorie target: Consume approximately your TDEE daily
  • Nutritional approach: Focus on balanced macronutrients and whole foods
  • Monitoring: Weigh yourself regularly and adjust intake if trends show change
  • Activity consistency: Maintain consistent exercise patterns to keep your activity factor stable

Weight maintenance requires regular monitoring as metabolism and activity levels can change over time, necessitating adjustments to your calorie intake.

Weight Loss

  • Moderate approach: Create a deficit of 300-500 calories below your TDEE for sustainable weight loss of 0.5-1 lb per week
  • Aggressive approach: Create a deficit of 500-750 calories for faster results (not recommended long-term)
  • Safety threshold: Never consume below your BMR without medical supervision
  • Exercise contribution: Aim for a combination of diet restriction (60-70%) and increased activity (30-40%)
  • Metabolic adaptation: Recalculate your BMR/TDEE every 10-15 pounds lost to account for metabolic changes

A moderate caloric deficit is generally more sustainable and helps preserve muscle mass during weight loss, leading to better long-term results.

Weight/Muscle Gain

  • Calorie target: Consume 300-500 calories above your TDEE
  • Protein intake: Increase to 1.6-2.2g per kg of body weight to support muscle synthesis
  • Training stimulus: Implement progressive resistance training to direct surplus calories toward muscle building
  • Nutrient timing: Consider strategic pre/post-workout nutrition for optimal results
  • Clean bulking: Focus on nutrient-dense foods to minimize fat gain during the surplus

A moderate caloric surplus combined with appropriate strength training creates the optimal environment for muscle growth while minimizing excessive fat gain.

Factors That May Affect Your BMR Beyond the Calculator

While the Mifflin-St Jeor equation provides an excellent estimate of BMR for most individuals, several factors can influence your actual metabolic rate that aren’t captured in the formula:

Body Composition

  • Muscle tissue burns approximately 6 calories per pound daily, while fat tissue burns only 2-3 calories
  • Two individuals with identical weight, height, age, and gender can have different BMRs if their body composition differs
  • Regular strength training can increase BMR by building metabolically active muscle tissue

DEXA scans, bioelectrical impedance, or other body composition assessments can provide insights into your muscle-to-fat ratio, helping refine BMR estimates.

Hormonal Factors

  • Thyroid hormones (T3, T4) significantly impact metabolic rate
  • Sex hormones (estrogen, testosterone) influence body composition and energy expenditure
  • Insulin sensitivity affects how efficiently your body processes and stores energy
  • Cortisol (stress hormone) can alter metabolism and promote abdominal fat storage when chronically elevated

Hormonal testing may be beneficial if you suspect imbalances could be affecting your metabolism.

Medical Conditions

  • Hypothyroidism or hyperthyroidism
  • Polycystic ovary syndrome (PCOS)
  • Cushing’s syndrome
  • Diabetes (both type 1 and type 2)
  • Chronic inflammation

If you’re following your calculated calorie targets but experiencing unexpected weight changes, consult with a healthcare provider to rule out underlying medical conditions.

Environmental and Lifestyle Factors

  • Sleep quality and duration (poor sleep can reduce BMR by 5-20%)
  • Environmental temperature (cold exposure can temporarily increase BMR)
  • Altitude (higher elevations may increase BMR by 10-15%)
  • Stress levels (chronic stress can alter metabolic function)
  • Previous dieting history (repeated severe calorie restriction can lower BMR)

Lifestyle optimization—particularly sleep quality and stress management—can help support healthy metabolic function.

Common Questions About BMR and TDEE

How often should I recalculate my BMR and TDEE?

You should recalculate your BMR and TDEE whenever significant changes occur in your body or lifestyle. Specifically, recalculate after: 1) Weight changes of 10+ pounds, 2) Age milestones (especially after 30, when metabolism naturally begins to decline), 3) Significant changes in activity level or exercise routine, 4) Starting or stopping medications that affect metabolism, or 5) Pregnancy and postpartum periods for women. Even without these specific changes, it’s good practice to recalculate every 3-6 months as part of regular health monitoring. For those actively losing or gaining weight, more frequent calculations (every 4-6 weeks) may be beneficial to adjust for the metabolic changes that occur during these processes.

Is BMR the same as Resting Metabolic Rate (RMR)?

While the terms BMR and RMR are often used interchangeably, they represent slightly different measurements. Basal Metabolic Rate (BMR) is measured under very strict conditions: after a full night’s sleep, in a fasting state (12+ hours), in a neutral temperature environment, and with the subject completely at rest. Resting Metabolic Rate (RMR) is measured under less restrictive conditions and typically accounts for the minimal energy required for daily functions while at rest, but not necessarily in the basal state. In practice, RMR is about 10-20% higher than BMR. For most people using estimates rather than direct measurements, the distinction is minimal, and the Mifflin-St Jeor equation provides a close approximation for either value. From a practical standpoint for nutrition planning, the small difference is rarely significant enough to warrant concern.

Why do I need to eat more than my BMR?

Consuming only your BMR in calories would provide just enough energy for your body to function at complete rest—essentially while lying motionless all day. This doesn’t account for any movement or activity, including basic activities like standing, walking, eating, or even the energy required to digest food. Consistently eating at or below your BMR leads to several negative consequences: 1) Nutritional deficiencies from inadequate food intake, 2) Muscle loss as your body breaks down tissue for energy, 3) Metabolic adaptation that lowers your BMR further, 4) Hormonal imbalances affecting thyroid function, reproductive health, and stress hormones, and 5) Psychological impacts including food obsession and disordered eating patterns. For healthy weight management, most experts recommend never consuming below BMR without medical supervision, and instead using your TDEE as the baseline for calculating appropriate calorie targets.

How can I increase my BMR naturally?

Several evidence-based strategies can help increase your BMR naturally: 1) Build muscle through strength training (each pound of muscle burns approximately 6 calories daily at rest), 2) Implement high-intensity interval training (HIIT), which creates an “afterburn” effect that elevates metabolism for 24-48 hours, 3) Consume adequate protein (0.8-1.0g per pound of body weight) to support muscle maintenance and the thermic effect of food, 4) Stay properly hydrated, as even mild dehydration can reduce metabolic rate by 2-3%, 5) Optimize sleep quality and duration, as sleep deprivation can lower BMR by up to 5-20%, 6) Manage chronic stress, which can normalize cortisol levels and prevent metabolic suppression, 7) Consume small, frequent meals if it helps you maintain consistent energy levels, and 8) Consider strategic caffeine intake, which can temporarily boost metabolic rate by 3-11%. Avoid crash diets and severe calorie restriction, which can lower your BMR by triggering your body’s starvation response.

How does BMR change with age?

BMR naturally declines with age due to several physiological changes. Research indicates that metabolic rate decreases approximately 1-2% per decade after age 20, with the rate of decline accelerating after age 40. This reduction occurs primarily due to: 1) Loss of muscle mass (sarcopenia), with the average person losing 3-8% of muscle per decade after age 30, 2) Hormonal changes, including declining levels of growth hormone, testosterone, and thyroid hormones, 3) Mitochondrial efficiency changes that reduce cellular energy production, 4) Decreased physical activity, which compounds the metabolic slowdown. The Mifflin-St Jeor equation accounts for this age-related decline by incorporating age as a negative factor in the formula. However, these changes aren’t inevitable—maintaining muscle mass through resistance training, staying physically active, consuming adequate protein, and getting proper sleep can significantly mitigate age-related metabolic decline.

Related Health Calculators

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Research and References

The science behind BMR calculation and the Mifflin-St Jeor equation is supported by extensive research:

  • Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.
  • Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789.
  • Frankenfield DC, Rowe WA, Smith JS, Cooney RN. Validation of several established equations for resting metabolic rate in obese and nonobese people. J Am Diet Assoc. 2003;103(9):1152-1159.
  • Johnstone AM, Murison SD, Duncan JS, Rance KA, Speakman JR. Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and circulating thyroxine but not sex, circulating leptin, or triiodothyronine. Am J Clin Nutr. 2005;82(5):941-948.
  • Gerrior S, Juan W, Basiotis P. An easy approach to calculating estimated energy requirements. Prev Chronic Dis. 2006;3(4):A129.

These studies demonstrate the validity of the Mifflin-St Jeor equation across different populations and its superiority to other predictive equations for estimating BMR in most individuals.

Health Disclaimer

The Mifflin-St Jeor BMR Calculator and accompanying information are provided for educational purposes only. This tool is not intended to replace professional medical advice, diagnosis, or treatment.

The calculated values represent estimates based on population averages and may not account for individual variations in metabolism due to genetics, medical conditions, or other factors. Individual energy needs may vary significantly from these estimates.

Always consult with qualified healthcare professionals before making significant changes to your diet, exercise regimen, or other lifestyle factors, particularly if you have existing health conditions, are pregnant or nursing, or are under 18 years of age.

Last Updated: March 29, 2025 | Next Review: March 29, 2026