I don't think the previous answers addressed your question. First, look at your "normal" densities. If you check out most film calibration articles or books, the recommended density for Zone V is in the 0.65 to 0.75 range, and the density for Zone VIII would be in the 1.25 to 1.35 range, IF you are using a diffusion enlarger head. The values for a condenser enlarger would be slightly lower.(posted 8373 days ago)If you develop your film for a longer time, the increase in density is not linear for all Zones, which is what allows you to achieve the desired effect of increasing the contrast of the negative relative to normal development. The Zone I will not change very much, Zone V will change more and Zone VIII will change even more.
To achieve an N+1 development, expose for Zones I and VII, and increase your development until the Zone VII exposures match your normal Zone VIII density. You will notice that Zone I does increase some, and you might want to decrease your initial exposure by an amount that brings Zone I into the normal 0.1 above base and fog density. That might only be 1/3 stop or so. Development for higher than N+1 would require greater reduction in exposure. How much reduction is a function of any particular combination of film and development method. You would have to experiment to find what YOU need to do. This can be tedious, but it can be rewarding, too. Don't get so caught up in worrying about it that you don't take pictures. That can happen.