Question
It's really different for everyone - but the one cold hard fact is that 3500 calories = 1 pound.
Now - the amount you burn depends on your basal metabolic rate - and that is determined by your height/weight, lifestyle and metabolism.
You can pry google basal metabolic rate and find lots of calculators and ways to get a good ballpark. I know my BMR is about 2700 cals a day. (based on my weight and the fact that I sit on my fat bum all day at work). So basically...anything I eat below 2700 contributes to my weight loss. So if I only eat 1000 a day then technically I should "burn" 11,900 a week (1700 X7) and loose 3.4 lbs. Seems pretty accurate because I do loose 3 or 3.5 lbs most weeks.
Do you use fitday? If so - go to the link on the right that says "activities" You can put in your lifestyle there and it will tell you your BMR - that's what I am going off of for myself.
Of course - you also have to consider that with WLS it has changed things a lot for us biologically. We absorb less cals because of the bypass but I also think it slows down our metabolism. But that's just my opinion.