I think it would need to come from your BMR value as you would need to be providing less than your body needs so that it starts taking from fat stores. If you are doing exercise though then that would affect things as that is beyond your bodys natural requirements right? So you could eat 1500 and lose 1kg a week if you did enough exercise to balance it or something...

I think 0.5-1kg a week weightloss is a good, reccommended amount for health reasons and because it becomes easier to maintain when it is done gradually? Doesn't it help to prevent your body going into starvation mode and trying to hold onto its current stores?

I'm not too sure so probably shouldn't add to the confusion haha but my best friend is a dietician and this is the vague information I've gleamed.