What Is the Mifflin–St Jeor Equation?
The Mifflin–St Jeor Equation is one of the most widely referenced and validated mathematical formulas in modern human energetics. Published in 1990 by Mark D. Mifflin, Sachiko T. St Jeor, and their research team at the University of Nevada School of Medicine in The American Journal of Clinical Nutrition, the equation predicts an individual's Resting Energy Expenditure (REE) based on body weight, stature (height), age, and biological sex.
Unlike historical equations from the early 20th century that evaluated small, specialized cohorts, Mifflin and colleagues developed their model from a diverse dataset of 498 healthy adult participants (251 males, 247 females) aged 19 to 78 years, with resting energy expenditure measured using indirect calorimetry.
A new predictive equation for resting energy expenditure in healthy individuals
Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. (1990)
The Mifflin–St Jeor Equations (1990)
Standard linear regression & Fat-Free Mass models published in AJCN
Contributes exactly +10 kcal/day per kilogram of total body mass.
Contributes exactly +6.25 kcal/day per centimeter of stature.
Reduces −5.0 kcal/day for every year of age to reflect metabolic shifts.
The Energy Architecture: From Metrics to REE & TDEE
How your individual physiological characteristics translate into daily resting and total expenditure
How to Calculate Mifflin–St Jeor Manually: Step-by-Step
To illustrate the exact arithmetic performed by our calculation engine, consider a 30-year-old male weighing 75 kg (165 lbs) with a height of 175 cm (5 ft 9 in):
REE = (10 × Weight) + (6.25 × Height) − (5 × Age) + 5
REE = (10 × 75) + (6.25 × 175) − (5 × 30) + 5
- • Weight contribution: 10 × 75 = +750.0 kcal
- • Height contribution: 6.25 × 175 = +1,093.75 kcal
- • Age adjustment: −5 × 30 = −150.0 kcal
- • Sex constant: +5.0 kcal
REE = 750 + 1,093.75 − 150 + 5 = 1,698.75 ≈ 1,699 kcal/day
REE vs. BMR vs. TDEE: Understanding Physiological Boundaries
In fitness media and nutrition forums, REE, BMR, and TDEE are frequently conflated. However, each metric describes a distinct physiological condition:
| Metabolic Quantity | Full Term | Testing & Fasting Conditions | Share of Total Daily Energy |
|---|---|---|---|
| REE (Mifflin–St Jeor) | Resting Energy Expenditure | Resting seated/supine, thermo-neutral room, 4–5h post-meal. Typically 3–10% higher than strict BMR. | ~60–75% of TDEE |
| BMR (Harris–Benedict) | Basal Metabolic Rate | Strict 12h overnight fast, measured immediately upon waking in thermo-neutral stillness. | ~60–70% of TDEE |
| TDEE | Total Daily Energy Expenditure | Full 24h expenditure: Resting Rate + Exercise + Non-Exercise Movement (NEAT) + Thermic Effect of Food (TEF). | 100% of Daily Output |
How Accurate Is the Mifflin–St Jeor Equation?
While many fitness calculators market Mifflin–St Jeor as “the single most accurate formula,” nutritional science demonstrates that all predictive equations carry inherent statistical error:
📊 Statistical Accuracy in General Adults
In systematic reviews (such as Frankenfield et al., 2005), the Mifflin–St Jeor equation estimated resting energy expenditure within ±10% of measured indirect calorimetry in approximately 70–80% of non-obese and obese healthy adults.
🏋️ Athletic & Muscular Populations
Because Mifflin–St Jeor relies solely on total body mass rather than body composition, it may underestimate resting metabolism in highly muscular athletes. For individuals with known lean body mass, body-composition formulas (like Katch–McArdle) often provide closer alignment.
⚠️ Responsible Interpretation Notice:
Your calculated REE is an educational statistical approximation, not a direct laboratory measurement. True individual metabolism varies based on organ mass, daily non-exercise physical activity, and historical nutritional intake.
Mifflin–St Jeor vs. Harris–Benedict: What's the Difference?
When comparing Mifflin–St Jeor with the Harris–Benedict Calculator, users often notice a 20–60 kcal difference in estimated baseline burn:
| Feature | Mifflin–St Jeor (1990) | Harris–Benedict (1919 / 1984) |
|---|---|---|
| Original Publication | 1990 (Am J Clin Nutr) | 1918/1919 (Carnegie Inst.) & 1984 revision |
| Primary Quantity | Resting Energy Expenditure (REE) | Basal Metabolic Rate (BMR) |
| Study Cohort | 498 modern adults (ages 19–78) | 239 historical adult subjects |
| Typical Difference | Tends to estimate 20–60 kcal lower | Tends to estimate 20–60 kcal higher |
The 1990 Fat-Free Mass (FFM) Equation & The ±10% Variance Band
In the original 1990 AJCN paper, Mifflin and St Jeor tested multiple regression models to identify the strongest biological driver of resting energy expenditure. They discovered that Fat-Free Mass (FFM) was the single best linear predictor ($R^2 = 0.64$):
While fat tissue expends approximately 4.5 kcal/kg/day, skeletal muscle and vital organs (liver, brain, heart, kidneys) expend between 13 and 200+ kcal/kg/day. By entering your estimated Body Fat %, our calculator unlocks this lean-mass equation, allowing athletic or lean individuals to bypass generalized height/weight assumptions.
Why We Display a ±10% Metabolic Confidence Band
Human metabolism is dynamic, not a fixed single number. Systematic reviews (Frankenfield et al., 2005) confirm that predictive equations are accurate within ±10% for approximately 80% of individuals. A calculated BMR of 1,699 kcal/day corresponds to a realistic physiological range of 1,529 to 1,869 kcal/day. Understanding this metabolic buffer prevents unnecessary dietary panic when scale progress fluctuates.
Frequently Asked Questions About the Mifflin–St Jeor Equation
What is the difference between Mifflin–St Jeor and Harris–Benedict?▼
Mifflin–St Jeor was published in 1990 from a cohort of 498 modern participants, whereas Harris–Benedict dates back to 1919. Because modern adult populations have different body compositions than 1919 cohorts, Mifflin–St Jeor typically produces a resting energy estimate that is 20–60 kcal lower than Harris–Benedict.
Is Mifflin–St Jeor a BMR or REE equation?▼
Scientifically, the Mifflin–St Jeor equation predicts Resting Energy Expenditure (REE), which is measured under resting conditions roughly 4–5 hours post-meal. Online, it is commonly referenced as a practical starting estimate for Basal Metabolic Rate (BMR).
How do I convert Mifflin–St Jeor REE to Total Daily Energy Expenditure (TDEE)?▼
To calculate TDEE, your resting REE is multiplied by a Physical Activity Level (PAL) multiplier between 1.2 (sedentary) and 1.9 (rigorous athletic training), or entered directly into our full TDEE Calculator.
Can I enter my weight in pounds and height in feet/inches?▼
Yes. You can switch between Imperial (lbs, ft/in) and Metric (kg, cm) at any time. Our engine automatically normalizes your entries internally to full mathematical precision.
Can this equation be used for teenagers and children?▼
The standard Mifflin–St Jeor study evaluated adults aged 19–78. In adolescents and children, active skeletal and tissue growth adds substantial caloric requirements that adult resting formulas do not reflect. Consult a qualified professional or guardian for youth nutrition tracking.
Why is my result different on other websites?▼
Variances across websites typically result from: (1) using a different underlying formula like 1919 Harris–Benedict or Schofield; (2) excessive rounding of constants; (3) rounding imperial conversions prematurely; or (4) applying hidden baseline activity factors without labeling them.
Peer-Reviewed References & Authoritative Literature
- Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2), 241–247. PMID: 2305711 • DOI: 10.1093/ajcn/51.2.241.
- Frankenfield, D., Roth-Yousey, L., & Compher, C. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 105(5), 775–789. PMID: 15883556 • DOI: 10.1016/j.jada.2005.02.005.
- Roza, A. M., & Shizgal, H. M. (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. The American Journal of Clinical Nutrition, 40(1), 168–182. PMID: 6741850 • DOI: 10.1093/ajcn/40.1.168.
- Schofield, W. N. (1985). Predicting basal metabolic rate, new standards and review of previous work. Human Nutrition: Clinical Nutrition, 39 Suppl 1, 5–41. PMID: 4044297.
- FAO/WHO/UNU (2004). Human energy requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. FAO Food and Nutrition Technical Report Series 1. Rome: FAO.