I use Myfitnesspal, here's the app:
http://www.myfitnesspal.com/iphoneI believe 3,500 calories (approximately) over or under your resting metobolic rate is 1 lb of weight (gained or lost)... as stated above this is usually accomplished by adding or reducing your caloric intake by 500 calories a day for a rate of change of about 1 lb per week.