About 3500 calories equals one pound. So, if you want to lose one pound a week, that would be the general formula to use. If you are cutting out 500 calories from your diet per day, that equals to 3500 calories for the week. If you can add in some exercise, that would increase the burn. However, I should say that I create a HUGE deficit every week and I don't burn according to that deficit. Maybe I'm a freak of nature
but my body doesn't do what it's "supposed to." I would imagine that this is the reason why so many people quit their "diets," because their bodies don't follow those rules of weight loss. Other times, they probably miscalculate how many calories they consume and maybe overestimate how many calories they burn. I don't know, but it sounds like you're on the right track!
First goal: under 180:
Second goal: 175 or below:
Third goal: 168 (no longer overweight):
Fourth goal: 160 or below:
Final goal: 145-155 (not sure if this will ever happen):