I was wonderign how much lb would i be able to go up on my lifts a month if were to do a heavy/light upper lower routine?
my calculator doesn't go up that high
How are we suppose to know?
It's pretty much impossible to predict, and there's a lot more to it than your split. In fact, that's one of the least significant aspects of your training.
But if you're training 4 times a week then an upper/lower split is a good way of organising your training, so give what you're suggesting a try and see for yourself how much your lifts increase