Calculate your Basal Metabolic Rate (BMR) - the number of calories your body needs at rest. Uses Mifflin-St Jeor Equation.
Calculate Basal Metabolic Rate using Mifflin-St Jeor Equation.
Your Basal Metabolic Rate (BMR) is the foundation of all calorie calculations—the minimum energy your body needs to perform essential life-sustaining functions while completely at rest. This includes breathing, blood circulation, cell production, brain function, nutrient processing, and maintaining body temperature. Even while sleeping, your body is burning calories to keep you alive.
Understanding your BMR is critical for any weight management, fitness, or nutrition goal. It typically accounts for 60-75% of your Total Daily Energy Expenditure (TDEE), making it the largest component of calories burned. Whether you're trying to lose weight, gain muscle, or maintain your current physique, knowing your BMR gives you a scientific baseline for calculating how much you should eat.
This calculator uses the Mifflin-St Jeor equation, which research published in the Journal of the Academy of Nutrition and Dietetics has shown to be the most accurate BMR formula for most healthy adults, with an accuracy rate of ±10% compared to indirect calorimetry (laboratory measurements).
Mifflin-St Jeor Equation (1990) — Recommended
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161
Harris-Benedict Equation (1919, revised 1984)
Men: BMR = 88.362 + (13.397 × weight kg) + (4.799 × height cm) - (5.677 × age)
Women: BMR = 447.593 + (9.247 × weight kg) + (3.098 × height cm) - (4.330 × age)
The Mifflin-St Jeor equation is preferred by the Academy of Nutrition and Dietetics as it accounts for modern body compositions and has been validated across diverse populations.
Multiply your BMR by the appropriate factor to estimate Total Daily Energy Expenditure (TDEE):
| Activity Level | Description | Multiplier | Example (1,600 BMR) |
|---|---|---|---|
| Sedentary | Little or no exercise, desk job | 1.2 | 1,920 kcal |
| Lightly Active | Light exercise 1-3 days/week | 1.375 | 2,200 kcal |
| Moderately Active | Moderate exercise 3-5 days/week | 1.55 | 2,480 kcal |
| Very Active | Hard exercise 6-7 days/week | 1.725 | 2,760 kcal |
| Extra Active | Athlete or physical job + training | 1.9 | 3,040 kcal |
Age: BMR decreases approximately 1-2% per decade after age 20, primarily due to loss of muscle mass (sarcopenia). A 50-year-old typically has a BMR 10-15% lower than a 25-year-old of the same size.
Muscle Mass: Muscle tissue is metabolically active, burning approximately 6 calories per pound daily at rest, compared to just 2 calories per pound for fat. More muscle = higher BMR.
Sex: Men typically have 5-10% higher BMR than women of equivalent weight due to greater muscle mass and lower body fat percentage on average.
Hormones: Thyroid hormones (T3 and T4) are primary regulators of metabolic rate. Hypothyroidism can reduce BMR by 15-40%, while hyperthyroidism can increase it by 10-50%. Testosterone, estrogen, and cortisol also influence metabolism.
Genetics: Studies suggest genetics account for 40-80% of the variation in BMR between individuals of similar age, sex, and body composition.
Body Temperature: Fever or cold exposure increases BMR. Each 1°F increase in body temperature raises BMR by approximately 7%.
Reference values based on average height and weight for each demographic:
| Age Group | Men (avg BMR) | Women (avg BMR) | Notes |
|---|---|---|---|
| 18-25 | 1,800-2,000 kcal | 1,450-1,650 kcal | Peak metabolic years |
| 26-35 | 1,700-1,900 kcal | 1,400-1,600 kcal | Slight decline begins |
| 36-45 | 1,650-1,850 kcal | 1,350-1,550 kcal | Muscle loss accelerates |
| 46-55 | 1,600-1,800 kcal | 1,300-1,500 kcal | Hormonal changes impact |
| 56-65 | 1,500-1,700 kcal | 1,250-1,450 kcal | Strength training helps |
| 65+ | 1,400-1,600 kcal | 1,200-1,400 kcal | Individual variation highest |
Based on average adult heights: Men 5'9" (175 cm), Women 5'4" (163 cm) with moderate body composition.
❌ Confusing BMR with TDEE: BMR is resting calories only—your actual daily needs are 20-90% higher depending on activity. Eating at BMR level will create a significant deficit for active people, potentially causing muscle loss and metabolic slowdown.
❌ Eating below BMR long-term: Consuming fewer calories than your BMR triggers metabolic adaptation. Your body thinks it's starving and reduces metabolism by 15-25%. Always eat at least your BMR, even when cutting.
❌ Underestimating activity level: Most people underestimate their activity. If you walk 10,000+ steps daily, take stairs, or have an active job, you're likely "Moderately Active" even without structured exercise.
❌ Overestimating activity level: Conversely, a 30-minute gym session 3x/week with a sedentary desk job is "Lightly Active," not "Very Active." Be honest about your overall daily movement.
❌ Ignoring body composition: Two people with identical weight can have vastly different BMRs. Someone with 25% body fat has a lower BMR than someone with 15% body fat at the same weight. Use the Body Fat Calculator for context.
❌ Not recalculating after weight change: Your BMR changes as your weight changes. Recalculate every 10-15 lbs lost or gained to ensure accurate calorie targets.
Sources & Methodology: BMR calculations use the Mifflin-St Jeor equation, validated by Mifflin MD, et al. in the American Journal of Clinical Nutrition (1990) and recommended by the American College of Sports Medicine (ACSM). Activity multipliers based on the Harris-Benedict activity factors as modified by the Academy of Nutrition and Dietetics. Reference ranges derived from NHANES data and the Journal of the Academy of Nutrition and Dietetics position paper on energy expenditure. Individual results may vary; for medical nutrition therapy, consult a registered dietitian. Calculator updated January 2026.
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. The most accurate formula is the Mifflin-St Jeor equation (1990): 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. The older Harris-Benedict equation (1919) is still used but less accurate: For men, BMR = 88.362 + (13.397 × weight kg) + (4.799 × height cm) - (5.677 × age). For women, BMR = 447.593 + (9.247 × weight kg) + (3.098 × height cm) - (4.330 × age). Research shows Mifflin-St Jeor is accurate within ±10% of laboratory measurements for most adults.
BMR (Basal Metabolic Rate) measures calories burned at complete rest—just to stay alive. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor representing your daily movement. TDEE = BMR × Activity Multiplier. The activity multipliers are: Sedentary (little/no exercise) = 1.2, Lightly Active (1-3 days/week) = 1.375, Moderately Active (3-5 days/week) = 1.55, Very Active (6-7 days/week) = 1.725, and Extra Active (athlete/physical job) = 1.9. For example, if your BMR is 1,600 calories and you exercise 3-5 days per week (moderately active), your TDEE is 1,600 × 1.55 = 2,480 calories/day. BMR typically accounts for 60-75% of TDEE.
The most effective way to increase your BMR is building lean muscle mass through strength training. Muscle tissue burns approximately 6 calories per pound daily, while fat burns only 2 calories per pound. Each pound of muscle gained increases your resting metabolism by 4-7 calories/day—that adds up! Other proven methods: (1) Eat adequate protein (0.7-1g per lb body weight)—protein has a high thermic effect, burning 20-30% of calories during digestion. (2) Stay active throughout the day—NEAT (non-exercise activity thermogenesis) can burn 200-500+ extra calories. (3) Get 7-9 hours of quality sleep—sleep deprivation can reduce BMR by 5-20%. (4) Stay hydrated—even mild dehydration slows metabolism. (5) Avoid prolonged extreme calorie restriction—eating below BMR triggers metabolic adaptation, potentially lowering your BMR by 15-25%.