confused...

Ok, I need some help. I have half a stone which follows me around. I currently need to shift all of it. For my height/weight etc, It says I need to eat 1200 calories a day, something which I generally struggle to do in that I don't like to eat that many but am slowly working out that that may be my problem, too few calories. So why is it, that if I do no exercise and consume my 1200 calories, my predicted weight loss is more than if I 'earn' calories by exercise and 'spend' them to meet my calorie goal? I am very confused..