Net calories

Options
Hi-
I am trying to figure my goals and I really want to lose as much weight as possible. I need help getting my thinking right. So when setting my net calories. (Total intake - calories burned) right? Why wouldn't I want this to be a negative number? Say I'm hoping to lose 1-2 lbs week so I need a 3500-7000 calorie deficeit right? I think I'm over thinking this and should let the computer do the work. I have a fitbit and it tells me I have burned x amout of calories today. So shouldn't I just eat the 500-1000calories less than amount burned? HELP!!