Among the many formulas used to estimate Basal Metabolic Rate and TDEE, the Mifflin-St Jeor equation stands out as the most validated and widely recommended by nutrition professionals, registered dietitians, and scientific bodies including the Academy of Nutrition and Dietetics. This guide explains exactly how it works, why it is considered the gold standard, and how to apply it to calculate your TDEE.
The History of the Mifflin-St Jeor Equation
The Mifflin-St Jeor equation was developed in 1990 by Dr. M.D. Mifflin and St. Jeor at the University of Nevada School of Medicine. The researchers recruited 498 adults (both obese and non-obese) ranging in age from 19 to 78 and measured their resting metabolic rate using indirect calorimetry — the gold standard for metabolic measurement. The resulting formula proved more accurate than the then-dominant Harris-Benedict equation, particularly for modern populations.
The Mifflin-St Jeor Formula
The equation calculates BMR (Basal Metabolic Rate) in kilocalories per day:
- 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
The only difference between the male and female formulas is the constant at the end (+5 for men, −161 for women), which accounts for the average metabolic difference between the sexes.
Step-by-Step Calculation Example
Example: Male
- Age: 32 years
- Height: 180 cm
- Weight: 85 kg
BMR = (10 × 85) + (6.25 × 180) − (5 × 32) + 5
BMR = 850 + 1,125 − 160 + 5 = 1,820 kcal/day
Example: Female
- Age: 28 years
- Height: 165 cm
- Weight: 62 kg
BMR = (10 × 62) + (6.25 × 165) − (5 × 28) − 161
BMR = 620 + 1,031.25 − 140 − 161 = 1,350 kcal/day
Converting Mifflin-St Jeor BMR to TDEE
BMR represents calories at complete rest. To estimate total daily needs, multiply by your activity factor:
| Activity Level | Multiplier | Example TDEE (1,820 BMR) |
|---|---|---|
| Sedentary | × 1.2 | 2,184 kcal |
| Lightly Active | × 1.375 | 2,503 kcal |
| Moderately Active | × 1.55 | 2,821 kcal |
| Very Active | × 1.725 | 3,140 kcal |
| Extra Active | × 1.9 | 3,458 kcal |
Mifflin-St Jeor vs. Other TDEE Formulas
| Formula | Year | Accuracy vs. Measured RMR | Best For |
|---|---|---|---|
| Mifflin-St Jeor | 1990 | ±10% (best in class) | Most adults |
| Harris-Benedict (Revised) | 1984 | ±10–15% | Historical reference |
| Katch-McArdle | 1996 | ±5–8% (if BF% accurate) | Athletes/bodybuilders |
| Schofield | 1985 | ±10–15% | Non-Western populations |
A landmark 2003 comparison study published in the Journal of the American Dietetic Association (Frankenfield et al.) found that the Mifflin-St Jeor equation predicted RMR within 10% for 82% of adults tested — more consistently than any other commonly used formula.
Limitations of the Mifflin-St Jeor Formula
Despite its accuracy for average populations, the formula has documented limitations:
- Body composition is ignored: The formula uses total body weight, not lean mass. A 90 kg athlete and a 90 kg sedentary person with very different body compositions will get the same BMR estimate, which is inaccurate. Use Katch-McArdle if you know your body fat percentage.
- Accuracy varies at extremes: The formula is less accurate for people with very high obesity (BMI >40) or very lean athletes (<10% body fat). It also shows reduced accuracy for people over 70.
- Ethnic variation: Studies have found the formula may slightly overestimate BMR in some Asian populations and slightly underestimate it in some African-American populations.
Practical Tips for Using the Mifflin-St Jeor TDEE
- Use your calculated TDEE as a starting estimate, not a fixed truth
- Track your weight daily and take weekly averages over 3 weeks at a consistent calorie intake
- If weight is stable, your actual TDEE matches your intake — adjust from there toward your goal
- Recalculate when your weight changes by more than 5 kg or your lifestyle changes significantly
Frequently Asked Questions
Is the Mifflin-St Jeor formula accurate for very overweight people?
Less so than for normal-weight individuals. The formula may overestimate BMR for those with very high obesity, because much of the excess weight is fat tissue (which burns fewer calories than muscle). The Katch-McArdle formula is more accurate if body fat percentage is known.
Can I use the Mifflin-St Jeor formula for kids?
No. The formula was validated for adults (19+). For children and adolescents, the Schofield or FAO/WHO/UNU equations are more appropriate, as they were specifically developed for pediatric populations.
Why does our TDEE calculator use Mifflin-St Jeor by default?
We use Mifflin-St Jeor as the default because it consistently shows the highest accuracy in independent validation studies and is the formula recommended by the Academy of Nutrition and Dietetics for clinical practice. You can also select Katch-McArdle in our advanced settings if you know your body fat percentage.
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