There is something called the Harris-Benedict formula that uses a mathematical formula to determine your caloric needs based on your sex, weight, and activity level; the result is known as your Basal Metabolic Rate. The U.S. government provides a chart of suggested daily caloric needs as part of the My Pyramid.gov Web site. Additionally, Calorie Count Plus allows you to type in your weight, activity level and weight loss goals and receive caloric intake recommendations when you sign up for a free account.
Once you know the number of calories you need in order to maintain your weight, you can create your own caloric goals for losing weight. It's up to you how many calories you cut from your daily diet. Remember, it takes a calorie deficit of 3,500 calories for you to lose a pound. Most people find it easiest and most effective to cut between 250 and 500 calories a day. Beware of cutting calories too low (below 1,200) as doing so can put your health at risk.