Monthly Stock Returns

Since I want this blog to be useful to people that aren't investment professionals - i.e., don't have a Bloomberg or other validated data sources available to them - I'm going to include comments about data sources. You can download a history of monthly prices from Yahoo, but you have to download dividend history separately, and put prices and dividends together on a spreadsheet to calculate total returns. I wondered if there was an easier way to get monthly returns. I googled "ibm monthly return history," and found the chart below on AOL.


However, AOL's returns for IBM don't match Bloomberg's returns for IBM. Bloomberg shows -0.92 for Jan 08, -1.43 for Oct 07, and -1.26 for Jun 07. I didn't go back any further. June and October 07 are off only a basis point, but Jan 08 is significant. The months with discrepancies aren't months with dividends, so it's not that. For months which do have dividends, only the price return is shown. Although AOL provides a nice table, these returns won't work for our purposes.