The Mifflin-St Jeor Formula

(W = weight in kg, H = height in cm, A = age in years)

Common Mistakes

• Overestimating activity level — most people are less active than they think; when in doubt, round down.
• Cutting calories too aggressively — deficits larger than 500-750 calories/day often backfire by slowing metabolism and causing muscle loss.
• Not recalculating TDEE as weight changes — a lighter body burns fewer calories, so your target should be revisited every 10-15 lbs lost.

Quick Reference

1 lb of fat ≈ 3,500 calories. A daily 500-calorie deficit ≈ 1 lb lost per week.

Frequently Asked Questions

Why do the male and female formulas differ?

Men typically carry more lean muscle mass relative to body weight than women on average, and muscle burns more calories at rest than fat — the formula's constant adjusts for this physiological difference.

Does age really affect metabolism that much?

Yes — BMR naturally declines with age as muscle mass tends to decrease, which is why the formula subtracts a small amount per year of age.