You can use this formula to determine percentage increase:

100(New Value - Old Value)/(Old Value)

Example: There were 200 customers yesterday, and 240 today:

100(240 - 200)/200 = (40/200) * 100 =

20% increase.

20% increase.

Example: But if there were 240 customers yesterday, and 200 today we would get:

100(200 - 240)/240 = (-40/240) × 100% =

A 16.6...% decrease.

A 16.6...% decrease.