Learn the daily calories needed to achieve your fitness goals. Your calorie requirements should be determined by your genetics, weight, activity level and fitness goals. There is a minimal caloric need for your body to function properly. Calorie needs is also slightly different for males and females. 

A larger individual will generally require more calories than a smaller individual.  A 150 pound male may only require 1400 calories a day while a 250 pound guy may require 1800 per day just to maintain enough energy to get through the day. The activity level of a person also determines how many daily calories are required. A female the exercises 5 days a week and jogs will require more energy than a person that lives a sedentary lifestyle. Your fitness goals also are a determinate in your calorie needs. If you are trying to lose weight, you may want to lower your calorie intake. If a male is trying to pack on muscle mass, he may decide to increase his calorie intake. You must be careful not to go to low because this can have a negative effect on your body functions.