Excel: Advanced Conditional Formula - Help

Thanks in advance to anyone who can help me with this. I need to adapt a spreadsheet so that the reults of a calculation move to different cells based on a specific parameter. For instance, if someone is set up for reoccuring billing every month and I want to move it to every 3 months, all I want to do is change 1 variable. This would be simple if only a couple individuals are involved and the patern is constant. However, thousands of people can be involved and there will an an attrition rate, wheras, for example, 20% drop after the 1st billing, then another 20% drop before the 2nd billing, etc. The total revenue each month will changed based on whether the interval between billings was 1, 2 or 3 months out. Since the spreadsheet will be quite large and I want to be able to run many scenarios, I want to be able to change only 1 variable to change the future results.

I've seen this done before and it's probably simple for some of you advanced users. I would appreciate any help in solving this or direction as to where I can find this answer. Thanks, Bry

 

Sounds like an IF statement is going to be involved but if you gave a few examples of what you want (such as: cust1 billed 1 monthly, stays as cust, needs to move to 3 monthly) it might help with figuring out what you want.