The Harris-Benedict equation is a calorie formula using the factors of gender, weight, height, and age to determine basal metabolic rate (BMR).  There is a shortcoming to this formula - it does not take into consideration lean body mass (LBM).  Therefore, this equation will be very accurate in all but the extremely muscular (the formula will underestimate calorie needs) and the extremely overweight (the formula will overestimate calorie needs).

The equation is different for men and for women