It would all depend on the lens. There are unfortunately no absolute rules for how much to shift focus with IR film.

However: Unless you use Kodak HIE it doesn't matter. All other films are only sensitive to near-infrared down to about 800nm, which is close enough to visible light that most lenses will be fairly wll corrected. I've shot the new MACO IR 820/400 with a Voiglšnder 21mm lens, nd everything was tack sharp. Of course the extreme DOF with a 21mm lens helped a lot