Question about Calories and Exercise

I have a question...I am 13 months post op and I was wondering if anybody knew or knows how many calories I should be intaking when I am exercising 60-90 minutes a day at a moderate pace and I'm buring off anywhere from 700-1000 calories. My diet right now consists of anywhere from 1200-1500 calories.I just want to make sure I'm not going to put myself into a starvation mode or worse where my body is eating up the muscle. Any input you have would be great! Thanks!