How the Mifflin-St Jeor Equation Works
The Mifflin-St Jeor equation calculates your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest just to keep you alive. It factors in gender, age, height, and weight. Your Total Daily Energy Expenditure (TDEE) is then calculated by multiplying BMR by an activity factor. This is the number of calories you need to maintain your current weight.
Published in 1990, Mifflin-St Jeor is considered the most accurate predictive equation for most people, outperforming the older Harris-Benedict formula. However, all equations are estimates. Your actual metabolic rate depends on factors no formula can capture: muscle mass, thyroid function, stress levels, sleep quality, and training history. Use the number as a starting point, then adjust based on real-world results over 2-3 weeks.
Setting Calorie Targets for Strength Athletes
For fat loss, a 300-500 calorie deficit is aggressive enough to see results without destroying training performance. Larger deficits lead to muscle loss, especially for lifters over 40 who already face anabolic resistance. For bulking, a 200-400 calorie surplus is sufficient — the "eat everything in sight" approach just builds body fat, not muscle.
After four decades of training, the biggest nutrition lesson is this: consistency beats precision. A roughly accurate calorie target followed consistently for months will always outperform a perfectly calculated target followed for two weeks before quitting. Track for long enough to learn your body's patterns, then use that knowledge to eat intuitively with periodic check-ins.