The Mifflin-St Jeor equation estimates your basal metabolic rate (BMR) from body weight, height, age and sex. Mifflin, St Jeor and colleagues published it in 1990, and today it is the basis of most calorie calculators.
The formula
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) - 5 × age (years) + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) - 5 × age (years) - 161
Example: A man weighing 80 kg, 180 cm tall and 30 years old gets 800 + 1,125 - 150 + 5 = 1,780 kcal BMR. With an activity factor of 1.55 that gives an estimated TDEE of about 2,760 kcal. These numbers are a worked example.
How accurate it is
A systematic review by Frankenfield and colleagues (2005) found that Mifflin-St Jeor predicts resting metabolic rate within 10 percent for more people than the other common equations. It is therefore considered the most reliable equation that needs no body fat measurement. Still, it misses by more for some people. On top of that comes the uncertainty of the activity factor, which is often larger than the error of the equation itself.
The equation does not know your muscle mass. For very muscular or very lean people, the Katch-McArdle equation, which starts from lean mass, can fit better.
A starting value, not the final answer
Use the equation for what it does well: a sensible starting value for the first two to three weeks. After that, your trend weight compared with your intake shows where your maintenance really is. Lean is law uses Mifflin-St Jeor as an estimate until there are enough food logs for the adaptive TDEE.