Mifflin-St Jeor Equation

The Mifflin-St Jeor equation (1990) revolutionized calorie calculation. Unlike the older Harris-Benedict formula, it uses modern metabolic data and shows 85–90% accuracy for most people. It remains the gold standard for predicting basal metabolic rate in healthy adults.

Historical context

Before 1990, the Harris-Benedict equation (1919) was the dominant formula for estimating BMR. But Harris-Benedict was developed using a small, homogeneous sample of mostly young men, and it systematically overestimates metabolic rate in modern populations. Dr. Michael Mifflin and Dr. Steven St Jeor recognized this limitation and designed a new study with 247 healthy adults of varying ages, weights, and body compositions. Their result — the Mifflin-St Jeor equation — cut the prediction error significantly and became the most widely adopted BMR formula in nutrition science, clinical dietetics, and fitness.

Mifflin-St Jeor equation formulas

For men:

BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age + 5

For women:

BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age - 161

The only difference between the men's and women's formulas is the constant at the end: +5 for men, −161 for women. This reflects average differences in lean body mass and body composition between sexes.

How Mifflin-St Jeor compares to Harris-Benedict

Developed in 1990 using modern metabolic data, Mifflin-St Jeor outperforms the 1919 Harris-Benedict equation. See our BMR equations comparison for details.

Mifflin-St Jeor example calculation

For a 35-year-old woman, 165 cm, 70 kg:

BMR = 10 × 70 + 6.25 × 165 - 5 × 35 - 161
BMR = 700 + 1,031.25 - 175 - 161 = 1,495 calories/day

With moderate activity (1.55): 1,495 × 1.55 = 2,317 maintenance calories.

Mifflin-St Jeor for different populations

The equation was validated on healthy, non-obese adults. It performs well for:

• General adult population: 85–90% accuracy for most people
• Overweight and obese individuals: slightly less accurate than for lean individuals, but still better than Harris-Benedict
• Older adults: reasonably accurate, though BMR naturally declines with age and muscle loss

It may be less accurate for:

• Very lean athletes: body fat percentage is low, and muscle mass is high
• Clinical populations: thyroid disorders, metabolic syndrome, or severe obesity
• Children and adolescents: still growing, with different energy needs

Accuracy discussion

Mifflin-St Jeor typically predicts BMR within ±10–15% of measured values in a lab. That is good enough for everyday use, but it is not perfect. Individual variation exists due to genetics, hormone levels, body composition, and adaptation. The best way to confirm your true maintenance is to track your weight and adjust intake based on real-world results for 2–3 weeks.

How to use Mifflin-St Jeor for TDEE

Once you have your BMR from Mifflin-St Jeor, multiply it by an activity factor to get TDEE:

The TDEE calculator automates this entire process. For a standalone resting number, use the BMR calculator.

Step-by-step calculation example

Let's calculate BMR and TDEE for a 28-year-old man, 178 cm, 82 kg, moderately active:

Step 1: BMR = 10 × 82 + 6.25 × 178 - 5 × 28 + 5
BMR = 820 + 1,112.5 - 140 + 5 = 1,797.5

Step 2: TDEE = 1,797.5 × 1.55 = 2,786 calories/day

He would eat 2,286–2,536 calories/day for weight loss, or 3,036–3,286 calories/day for muscle gain.

Why Mifflin-St Jeor is the standard

Research validates its accuracy:

• 85–90% accurate vs measured metabolic rate
• Lower standard error than Harris-Benedict
• Works across diverse populations
• Used by our BMR calculator and all our guides