How many Calories do I Need a Day?
Multiply your target Weight by 10. The result is an estimate of the calories you need for basic metabolic functions (enough energy for breathing, sleeping, etc).
Add to the number just calculated one of the following activity factors. (Pick the range that fits your lifestyle on a day to day basis):
Sedentary: Add 300 (limited exercise if any; i.e. reading a book, watching TV, driving a car, shopping, and light walking).
Moderately Active: Add 500 (light activity; i.e. walking, fishing, golfing, pleasure cycling, dancing, calisthenics, and volleyball).
Extremely Active: Add 700 (extremely active; i.e. jogging, running, football, basketball, swimming, scuba, and cross country skiing).
(Source: http://www.acumedic.com )