sorry n2l you posted as I was. All these sites will add your exercise cals burnt to your gross cals for the day. You would have set your goal weight and they will work out the amount of cals (gross cals) that you can eat in that day to acheive it at about 500g loss a week or so. They will work out the optimum calorie deficit from your BMR to lose at that rate, i.e. your BMR may be 2000 but they will put you on a daily intake of 1500, if that makes sense. So even if you eat back your calories and your net total for the day is 1500, you should still lose weight.

BUT having said that, I still didn't eat back my exercise calories.