Look into table calculations (difference and percentage difference). It's hard without seeing your data, but assuming you have the Year/Month in the columns and are summarizing $, you just need to do table calculations on the dollars field. It's worth noting that you may need to change how the table calculations are viewed (down vs across).
Thanks a bunch for replying... I tried your suggestion and could not come to the desired result... See attached Jpeg for more... Care to look at it and suggest again? Thanks a bunch