First of all, you actual activity level and metabolism. If your metabolism is high then you will lose more calories, but if you have a sedentary life you will not take advantage of you high metabolism.
Doctors have decided to use for reference the BMI: basal metabolic rate. The average number of calories one consumes for a given weight and age. It is known that a young man burn more calories than an older one.
To figure out how many calories you should eat a delay click this link: how many calories should I eat a day