I know it's possible to calculate how much growth in height you have left by these stages. But is it possible I can calculate how much weight I have left to gain?
There is no absolute upper bound to your weight.
You can overeat, put on oodles of fat, and be hundreds of pounds.
You can also workout and build your muscles up. You'll look a whole lot better, but the size of your muscles will depend on how much you work out.