Breast Feeding and working out

OK so I am still breast feeding, my son is now 4 months old. I only give him one formula bottle a day so that he sleeps a little more at night. I know I saw a fee on here that you burn about 500 calories exclusively breast feeding, but what I want to know is there a way to break it down a little more seeing as how every one is different. while yes I do sometimes throw in a baby food and then the formula bottle at night he is still a big eater and I am feeding him still about 5 times a day from the breast. Sorry for the personal info I was just trying to get more of a grip on the breast feeding and working out scenario.