CalcMifflin-St Jeor BMR Calculator
Mifflin-St Jeor BMR Calculator. Free online calculator with formula, examples and step-by-step guide.
BMR Calculator (Mifflin-St Jeor): Estimate Your Resting Calorie Needs
The Mifflin-St Jeor BMR calculator estimates your basal metabolic rate, the number of calories your body burns at complete rest just to sustain vital functions like breathing, circulation, cell production, and brain activity. The Mifflin-St Jeor equation, published in 1990, is now the formula of choice recommended by the American Dietetic Association for healthy individuals. It replaced the older Harris-Benedict equation because it was developed using a more modern and diverse population and has been validated in numerous clinical studies as the most accurate for the general population. Whether you are planning a weight loss diet, designing a muscle-building meal plan, or simply curious about your body's energy needs, this calculator provides your baseline calorie requirements.
Mifflin-St Jeor BMR Equation
Men: BMR = (10 × Weight) + (6.25 × Height) − (5 × Age) + 5
Women: BMR = (10 × Weight) + (6.25 × Height) − (5 × Age) − 161
Weight is in kilograms (kg), height in centimeters (cm), and age in years. All results are in kilocalories per day (kcal/day). The formula accounts for three key factors: body size (weight and height), which determines the amount of metabolically active tissue; age, which affects metabolic rate because lean mass naturally declines over time; and sex, reflected in the constant term (+5 for men, −161 for women). The larger female constant reflects the generally higher body fat percentage and lower muscle mass of women compared to men of the same weight and height.
The Mifflin-St Jeor equation estimates BMR within 10% of measured values for approximately 82% of the general population, making it the most clinically validated predictive equation available. However, it does not account for body composition (muscle-to-fat ratio), so a very muscular individual may have a BMR significantly higher than predicted, and an obese individual with very low muscle mass may have a lower BMR. For these cases, the Katch-McArdle formula, which uses lean body mass instead of total weight, can provide a more accurate estimate.
Worked Examples
Example 1: Overweight Male Starting Weight Loss
A 38-year-old man weighs 105 kg, is 178 cm tall, and wants to start a weight loss program.
Calculation: BMR = (10 × 105) + (6.25 × 178) − (5 × 38) + 5
= 1050 + 1112.5 − 190 + 5 = 1,978 kcal/day
His BMR of 1,978 kcal means his body needs nearly 2,000 calories daily just to maintain basic life functions. With a sedentary desk job (activity factor 1.2), his TDEE is 1,978 × 1.2 = 2,374 kcal/day. For safe weight loss of 0.5 kg per week, he should target a 500 kcal deficit, consuming approximately 1,874 kcal/day. This is slightly below his BMR, which is acceptable under medical supervision for short-term weight loss in obesity. A protein intake of 1.6–2.0 g per kg of body weight (168–210 g/day) would help preserve muscle mass during the deficit.
Example 2: Active Woman Adjusting for Muscle Gain
A 25-year-old woman weighs 63 kg, is 165 cm tall, weighs 63 kg, and strength trains 5 times per week.
Calculation: BMR = (10 × 63) + (6.25 × 165) − (5 × 25) − 161
= 630 + 1031.25 − 125 − 161 = 1,375 kcal/day
Her BMR of 1,375 kcal is the baseline. With very active exercise (factor 1.725), her TDEE = 1,375 × 1.725 = 2,372 kcal/day. For muscle gain, she should consume a surplus of about 300 kcal above TDEE, targeting 2,672 kcal/day with at least 1.6–2.2 g/kg of protein (100–140 g/day). Her actual BMR may be slightly higher than the Mifflin-St Jeor prediction because her higher muscle mass from strength training increases resting energy expenditure beyond what the formula predicts for the average woman of her weight and height.
Common Uses
- Establishing baseline calorie requirements for weight management programs including weight loss, maintenance, and muscle gain phases
- Clinical nutrition planning for patients with metabolic disorders, thyroid conditions, or eating disorder recovery protocols
- Comparing BMR predictions across different formulas (Mifflin, Harris-Benedict, Katch-McArdle) to understand which is most appropriate for a given body type
- Setting minimum safe calorie thresholds for very-low-calorie diets (VLCDs) to prevent metabolic slowdown and gallstone formation
- Calculating macronutrient distribution by first establishing total calorie needs based on BMR times activity factor
- Monitoring metabolic health by tracking changes in measured versus predicted BMR during weight loss to detect excessive metabolic adaptation
Common Mistakes
- Consuming fewer calories than BMR for extended periods without medical supervision, which triggers metabolic adaptation that reduces the body's energy expenditure by 10–20%
- Using the Mifflin-St Jeor equation for individuals with high muscle mass or obesity without considering that body composition significantly affects accuracy
- Applying the formula with weight in pounds and height in inches instead of metric units, producing BMR values that can be off by hundreds of calories
- Assuming BMR is static when it changes with weight loss (decreases by about 100 kcal per 10 kg lost), requiring recalculation every 5–10 kg of weight change
- Confusing BMR with resting metabolic rate (RMR), which is typically 10–20% higher because it is measured under less strict conditions
Pro Tip
The Mifflin-St Jeor equation is excellent for group estimates but can miss individual variation by 200–400 kcal/day. To find your true BMR, use this calculator as a starting point, then track your weight and calorie intake precisely for 3–4 weeks using a food scale and tracking app. If your weight is stable, your actual TDEE equals your average daily calorie intake. Divide your TDEE by your estimated activity factor to back-calculate your personal BMR. For example, if you maintain on 2,400 kcal/day with a moderately active lifestyle (factor 1.55), your actual BMR is 2,400 / 1.55 = 1,548 kcal/day. This personalized value is more useful for precise diet planning than any population-based formula.
Frequently Asked Questions
The equation was developed from a primarily Caucasian population. It overestimates BMR by 5–8% in African Americans and underestimates by 3–5% in some Asian populations. Accuracy varies for Hispanic and South Asian individuals. Indirect calorimetry is the gold standard when precision matters.
For weight loss, eating back 50–75% of exercise calories helps maintain energy. For maintenance, eat back 100%. For muscle gain, eat back 100% plus a surplus. Calorie trackers often overestimate burn by 20–40%, so be conservative.
BMR declines 1–2% per decade after 20, accelerating after 40 due to muscle loss (sarcopenia). Mifflin-St Jeor accounts for age linearly, but actual decline may be non-linear. Resistance training can mitigate about half of age-related BMR decline.
Use TDEE, not BMR, as your starting point. A safe deficit is 300–500 kcal below TDEE for about 0.5 kg/week loss. Multiply BMR by activity factor (1.2 sedentary to 1.9 very active) to estimate TDEE. Going below BMR without supervision is not recommended.