Linking some old conversations on this topic to here. It hasn't been used in a while but, may be informative too.
Deciding on your goal weight
There is another conversation out there too. I will try to find it and link it here.
I decided on my goal weight based on an arbitrary number. I hadn't been below 175 in so very long. I just picked a number that was "overweight" for my height based on a chart for height and bone size. Then decided, when I get there I will pick my end goal. If I was small enough to be happy and had a low enough body weight at that point, I would stop.
It was a pencil mark on paper type of thing. It could always be erased and redone.