I am doing an addition and I think I am going to do soemthing where the floor joist sticks out about 4 feet past the wall for like a little deck that comes out of my room with no poles underneath, How far does the floor joist have to go inward to safely support this?

First those designs are prone to leaking. You need great flashing details to make sure that they are a path for water into the house and that they exposed parts don't rot.

And with cantalever of that much the designed needs to be engineered.