Your calorie needs are based on your basal metabolic needs (calories to keep you alive in a resting state), the calories you burn through your daily activity, and the calories you burn through planned exercise.
To see how the formulas work and your calorie range is determined, check out this SP article. www.sparkpeople.com/resource/calorie_calcu
If you have additional questions about all this...please let me know.
SP Dietitian Becky