Last updated: May 2026
Mifflin-St Jeor Calculator: The Most Accurate BMR Formula Explained
The Mifflin-St Jeor equation is the most widely validated formula for estimating basal metabolic rate (BMR) in healthy adults. Developed in 1990 by M.D. Mifflin and S.T. St Jeor, it consistently predicts BMR within 10% of direct laboratory measurement — outperforming the Harris-Benedict equation that had dominated since 1919.
TDEE Calculator
Enter your weight, height, age, and activity level to calculate your BMR and total daily calorie needs using the Mifflin-St Jeor equation.
The Mifflin-St Jeor Formula
The equation uses weight (kg), height (cm), and age (years). There are separate formulas for men and women:
Men:
BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women:
BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
The result is your resting energy expenditure in kilocalories per day — the number of calories your body burns with no activity whatsoever.
Step-by-Step Example
A 36-year-old woman, 165 cm tall, weighing 65 kg:
- Weight component: 10 × 65 = 650
- Height component: 6.25 × 165 = 1,031.25
- Age component: 5 × 36 = 180
- Female constant: −161
- BMR = 650 + 1,031.25 − 180 − 161 = 1,340 kcal/day
A 40-year-old man, 178 cm tall, weighing 82 kg:
- Weight component: 10 × 82 = 820
- Height component: 6.25 × 178 = 1,112.5
- Age component: 5 × 40 = 200
- Male constant: +5
- BMR = 820 + 1,112.5 − 200 + 5 = 1,737.5 kcal/day
Converting Imperial Units
If you have weight in pounds and height in inches, convert first:
- Weight: divide pounds by 2.205 to get kg (180 lbs ÷ 2.205 = 81.6 kg)
- Height: multiply inches by 2.54 to get cm (70 in × 2.54 = 177.8 cm)
From BMR to TDEE: Activity Multipliers
BMR is your calorie need at complete rest. To find your Total Daily Energy Expenditure (TDEE) — the actual calories you burn living your life — multiply BMR by your activity factor:
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, no structured exercise | 1.2 |
| Lightly active | Light exercise 1–3 days/week | 1.375 |
| Moderately active | Moderate exercise 3–5 days/week | 1.55 |
| Active | Hard exercise 6–7 days/week | 1.725 |
| Very active | Physical job + hard daily training | 1.9 |
Example continued: The 36-year-old woman above (BMR 1,340) exercises moderately 4 days per week.
TDEE = 1,340 × 1.55 = 2,077 kcal/day
This is her maintenance calorie level — the amount she needs to eat to keep her current weight stable.
Why Mifflin-St Jeor Replaced Harris-Benedict
The Harris-Benedict equation was the standard for 65 years before Mifflin-St Jeor. A systematic review comparing four predictive equations (Frankenfield et al., 2005, Journal of the American Dietetic Association) found that Mifflin-St Jeor was more likely to predict resting metabolic rate within 10% of that measured by indirect calorimetry than any other equation.
The key differences:
- Harris-Benedict (original 1919) overestimates by 5–15% for most modern adults — possibly because the study population was more active than the average person today
- Harris-Benedict (revised 1984, Roza-Shizgal) improved accuracy but still lags behind Mifflin-St Jeor in systematic comparisons
- Mifflin-St Jeor was developed from a larger, more representative population and is validated across a wider BMI range
When Mifflin-St Jeor Is Less Accurate
No formula accounts for individual variation perfectly. Mifflin-St Jeor tends to be less accurate in:
- Athletes and highly muscular individuals: The equation doesn’t account for body composition. Two people with the same weight, height, and age but very different muscle-to-fat ratios will get the same BMR estimate — even though muscle burns more calories at rest than fat. The Katch-McArdle formula, which uses lean body mass, is more accurate in these cases.
- Severely obese individuals: Overestimates BMR because adipose tissue has lower metabolic activity than the mixed-tissue assumptions built into the formula
- Elderly adults: Metabolic rate declines with age partially due to muscle loss; the linear age coefficient may not fully capture this
Using Your Result for Weight Goals
Once you have your TDEE from the Mifflin-St Jeor calculation:
- To lose fat: Eat 300–500 calories below TDEE. This produces 0.5–1 lb of fat loss per week without aggressive restriction.
- To maintain weight: Eat at TDEE.
- To gain muscle: Eat 200–350 calories above TDEE. Keeps fat accumulation minimal while supporting muscle protein synthesis.
Treat your calculated TDEE as a starting point, not a precise measurement. Track your weight for 2–3 weeks at the calculated intake. If weight is moving faster or slower than expected, adjust by 100–200 calories and reassess. All BMR formulas carry a ±10–15% margin of error; your body’s response is the most accurate feedback available.
Calculate Your BMR and TDEE
The TDEE calculator uses the Mifflin-St Jeor equation to calculate your BMR and multiply it by your activity level — giving you your daily calorie target in one step.
