Formula Imput - Which Way Is More Effective

I am looking to do a calculation that in excel would be a snap, but im looking to do it in the access database for the functionality that comes with it. I have a bunch of Agent codes and with each is associated a certain percentage split between them. So for example: 123 = 40% agent A and 60% agent B. These codes are listed in a dropdown menu so upon selection i would hope the formula would apply. There are maybe 15-20 of these codes, and they range from 1-3 agents. Would it be easiset to do a ton of If statements in an unbound text box? OR would it be easier to make a calculate button with If statements to calculate upon click. A brief exmple either way (or any orther ways that are better yet) would be greatly appreciated.

Once again what im looking for (abridged version):

1. pick the code
2. Input doller amount
3. Have it autocalc (if possible) or just calc on click

Also to be noted: the percentages are being taken of of a manually input percentage depending on other factors. So in essence the fields to be worried about are Initial doller amount, percent of that, and then the percent split off of that number. Thanks in advance!


-Bob