calc percentages of difference when entries are negative to positive or pos to neg, etc

Hi Todd- perhaps (in C2):
=B2/A2-1

It might be more of a math question than an Excel question.

The standard "percent difference/change" formula is (b-a)/ABS(a) (which is algebraically equivalent to leelnich's formula when both values are positive). I think this formula works well when both values are positive or when both values are negative. The real challenge is that it doesn't work very well when one value is positive and one is negative. When the signs are different, you can have scenarios where the percent change gets smaller as the difference between the values gets larger. This tends to make interpreting the percent change difficult, since one can no longer infer "larger/smaller" change based on the result. I recommend that you think very carefully about what you are trying to do here so you can come up with a way to measure whatever you need to measure here. Of course, if you already know how you want to calculate this quantity, let us know and we can help you program that into Excel.

Spreadsheets don't do magic, and MSFT's programmers (generally) implement consensus "best" formulas and algorithms. In this case, I am not aware of any consensus on how to calculate percent change/difference when the values are opposite sign (except maybe "percent change is not defined when values are of opposite sign"). I am afraid you are going to be disappointed in this case. You will need to come up with your own definition/formula for percent change that will "correctly" measure a meaningful quantity for your data. That probably means considering what kind of data you have, what the difference really means, what kind of analysis are you trying to do, and how will this "percent change" quantity help in making that analysis.