In the spreadsheet below, I have first calculated the beta for Apple (AAPL) using the S&P500 as my market return, basing my beta on 5 years of monthly returns for Apple and the S&P500, then adjusting all of these returns to real returns by subtracting out the 30-Yr Zero Coupon U.S. T-Bond. I have outlined this technique in another of my blog posts: How to use the CAPM and beta

My calculated beta for Apple (1.29) is in cell C5 of the Analysis worksheet. I checked this against Google’s reported beta for Apple (1.32), and Yahoo’s reported beta of 1.42. As I have commented on in previous blog posts, Yahoo’s beta’s are not correct, while Google’s beta’s are correct, at least based on the methodology that I choose to use when determining my betas.