The Mifflin-St Jeor equation, explained

The equation

Where BMR is in kcal/day. TDEE = BMR × activity factor.

Where it comes from

Mifflin, St Jeor, Hill, Scott, Daugherty, and Koh published it in 1990, “A new predictive equation for resting energy expenditure in healthy individuals”, American Journal of Clinical Nutrition 51(2):241–247 (PMID 2305711). It was built from calorimeter data on 498 healthy subjects and was introduced with Harris-Benedict data for comparison.

Why it is the default

• Most accurate for modern populations: the American Dietetic Association's evidence analysis of popular equations found Mifflin-St Jeor most likely to predict RMR within 10% of measured values.
• Simple inputs: weight, height, age, sex — no lab data needed.
• Outperforms the 1919 Harris-Benedict equation, which over-predicts for many modern body sizes.

Worked example

A 30-year-old man weighing 80 kg at 180 cm:

BMR = (10 × 80) + (6.25 × 180) − (5 × 30) + 5 = 800 + 1,125 − 150 + 5 = 1,780 kcal/day

Limitations

• Population estimates, not individual measurement like indirect calorimetry.
• Less accurate at very high or very low body weights, or unusual body compositions.
• Does not capture metabolic adaptation during prolonged dieting.
• When you know your body fat %, Katch-McArdle and Cunningham use lean mass and are often closer.

Calculate with Mifflin-St Jeor now