1,618
kcal/day
2,507
kcal/day
2,007
kcal/day
1,757
kcal/day
1,618
kcal/day
2,507
kcal/day
2,007
kcal/day
1,757
kcal/day
The Mifflin-St Jeor equation, published in 1990 by M.D. Mifflin and S.T. St Jeor in the American Journal of Clinical Nutrition, is now recognized as the gold standard for estimating resting energy expenditure in healthy adults. In 2005, the American Dietetic Association (now the Academy of Nutrition and Dietetics) reviewed all major BMR prediction equations and concluded that Mifflin-St Jeor was the most accurate, predicting measured resting metabolic rate within 10% for the largest proportion of individuals tested.
The equation was developed from a study of 498 healthy subjects (247 females, 251 males) ranging in age from 19 to 78 years and in BMI from 15 to 42 kg/m squared. The researchers used indirect calorimetry to measure actual resting metabolic rate and then derived regression equations relating these measurements to height, weight, age, and sex. The resulting equation is mathematically simpler than the Harris-Benedict formula while being more accurate, particularly for overweight and obese individuals.
What makes the Mifflin-St Jeor equation superior is its development using a more contemporary and diverse population than the original Harris-Benedict study from 1918. The subjects in the Mifflin study were measured in 1990, reflecting modern lifestyles, body compositions, and nutritional patterns. This temporal advantage means the equation is better calibrated to current populations who tend to be less physically active and carry more body fat than early 20th century populations.
The equation takes the form: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age(years) + s, where s is +5 for males and -161 for females. The 166-calorie difference between genders reflects the average difference in lean body mass between men and women of similar size. The negative age coefficient (-5 per year) captures the decline in metabolic rate with aging, primarily due to progressive loss of metabolically active lean tissue.
This calculator computes your Mifflin-St Jeor BMR and TDEE, then provides practical deficit recommendations for weight management. Importantly, the deficit values are floored at your BMR — the calculator will never recommend eating below your basal metabolic rate, which would risk metabolic adaptation and muscle loss. Use this as your primary calorie estimation tool and fine-tune based on real-world results.
The Mifflin-St Jeor equation: Males: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age(y) + 5. Females: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age(y) - 161. TDEE = BMR x Activity Factor. Mild deficit = TDEE - 500 (never below BMR). Moderate deficit = TDEE - 750 (never below BMR). This ensures you never eat below your basal metabolic requirements.
The Mifflin-St Jeor BMR is your estimated resting energy expenditure. TDEE is your total daily needs. A 500 kcal deficit produces ~0.5 kg/week loss, and 750 kcal deficit produces ~0.75 kg/week loss. Note the floor at BMR: if the deficit would push intake below BMR, the calculator limits to BMR, indicating that your activity level may need to increase to achieve the desired deficit safely.
Inputs
Results
BMR 1,718, TDEE 2,964. A 500-cal deficit = 2,464 kcal/day, comfortably above BMR.
Inputs
Results
BMR 1,289, TDEE 1,547. Both deficit levels are floored at BMR (1,289) because TDEE is too low for safe deficits.
A 2005 review by the American Dietetic Association found Mifflin-St Jeor predicted measured resting metabolic rate within 10% for more individuals than any other equation, including Harris-Benedict. It was developed with a more modern population sample and uses a simpler, more accurate formula.
The +5 for males and -161 for females accounts for the average difference in metabolic rate between genders beyond what height, weight, and age explain. This 166-calorie difference reflects higher lean mass in males, which drives a higher BMR.
Eating below BMR for extended periods risks muscle loss, metabolic adaptation, nutritional deficiencies, hormonal disruption, and decreased immune function. The calculator floors deficit recommendations at BMR to prevent these harmful outcomes.
A 500 kcal daily deficit produces approximately 0.5 kg (1 pound) of weight loss per week, assuming no metabolic adaptation. Actual results may vary as the body adapts to lower intake over time. Reassess every 2-4 weeks.
Mifflin-St Jeor may underestimate BMR for very lean, muscular individuals because it uses total body weight rather than lean mass. For bodybuilders or very lean athletes, the Katch-McArdle equation (which uses lean body mass) may be more accurate.
No, this equation is not validated for pregnant or lactating women. Pregnancy increases metabolic demands by approximately 300 kcal/day in the second trimester and 450 kcal/day in the third trimester. Consult your obstetrician for appropriate calorie recommendations.
BMR varies significantly between individuals due to differences in lean body mass, height, age, and genetics. A 6-foot, 25-year-old male athlete will have a much higher BMR than a 5-foot-2, 50-year-old sedentary female, even at the same body weight.
Caffeine temporarily increases metabolic rate by 3-11%, peaking about 1-2 hours after consumption. However, regular users develop tolerance. The Mifflin-St Jeor equation does not account for caffeine intake, as it was measured in a fasted state.
TEF (approximately 10% of calorie intake) is implicitly included in the activity factor multiplication. When you eat at your calculated TDEE, the energy needed to digest that food is already accounted for in the total estimate.
For weight loss or gain goals, tracking calories (at least for 2-4 weeks initially) helps calibrate your intake. Once you develop an intuitive sense of portion sizes and calorie density, many people can transition to mindful eating while monitoring weekly weight trends.
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