I've confused myself!

I just started doing the elliptical on top of doing the 30-Day Shred, and I am having trouble figuring out how many calories I need to eat in a day now. I always go on freedieting.com to find how calories I should eat per day, so I eat about 1600 calories a day. However, adding in 500-1000 calories more that I am burning, should I up my calorie intake? I don't want to get sick or anything, but I also don't want to up my calories if I shouldn't.
Advice??