I don't Fitday. It does my head in

It works for some people and not for others.
First rule of weight loss - do what works for you!
I started by diarying everything I ate and using an old fashioned calorie counter book to total it up. I hit for 1400 -1600 a day depending on my calorie output, and I aim to hit the gym 5 - 6 days a week. However I am not overly active during the day.
Your not going to get mathematically correct answers, coz there aren't any! Too many variables. Then you'll get weeks where you are doing everything right, and you don't lose, then you'll have weeks where you have been a bit naughty and you lose.
Try not to get caught up in the numbers, but learn to live a healthy lifestyle, and the weight loss will start to fall in to place.