I think the forumla is:
((<NewValue> - <OldValue>) / <OldValue> * 100)
* Positive result indicates an increase
* Negative result indicates a decrease
eg. Old Value = 100, New Value = 125,
((125 - 100) / 100 * 100) = 25
therefore: increase from 100 to 125 is a 25% increase.
eg. Old Value = 125, New Value = 100,
((100 - 125) / 125 * 100) = -20
therefore: decrease from 125 to 100 is a 20% decrease.
-genius_at_work