From the horse's mouth, or a$$ depending on your perspective, a DO a few years back said the number is 70%.
Now how they calculate that is another matter. Do they count every kid that is an UBP? Just those that get dunked then leave? Whatever the method, too many are leaving and the GB recognized their little cult will die a long slow death if they can't turn this around.
So they are trying to get kids dunked earlier, keep them away from college, and off of the internet. (Good luck with that GB)
When they start encouraging JWs to have kids, we will know they are really desperate.