Thank you very much for your answer!    There are some things that you should know for the return :  First there is no return for the first date (here 25 May 2012)  Second the calculation for the return is :  {(Price of the day (t) - Price of the previous day (t-1))/(Price of the previous day (t-1)} * 100  Therefore the return for 28 May 2012 for the CAC will be : {(3042-3047)/3047} * 100 = -0,16%   I don't know if it would be easier to add a step which would be to calculate the lag of the values, therefore :  (Price of the day (t) - Price of the previous day (t-1)) And add this calculation to a new column for each stock.    Also, I was wondering if maybe if it would be easier to create a new table with the new columns that we want instead of adding new columns so the existing data set would not be destroyed.    I will try to see if SASHELP.Stocks can answer my questions !  ... View more