There are lots of rules about financial aid that are good to know. The NPCs vary among schools because every school has their own rules about how merit and need-based aid is allotted to their students. If that wasn’t the case, we would only need one NPC that covers every college in the country. The accuracy of each NPC depends on how closely it mimics the actual formula that the school uses. This varies widely. Accurate NPC results also depend on the accuracy of the information that the user enters.