Compare stock prices over time

Hi ,

I have hundreds of clients who have different accounts with varying securities such as stocks and mutual funds.
I pulled a report which I was able to format so that each position (stock/MF) in the account is visible with the account holder's name and account number, etc.

How do I get excel to compare the price for each stock or MF in each account from Jan 1 and Aug 4 so I can find out how the stock or MF performed?

I was thinking if I could say something like (IF x and y are true between the spreadsheets on a particular row then subtract this price from that price and I would get my answer - but I don't know how to do that and I don;t even know if that is the best way)

thanks