Percentage decrease - Math Central

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Question from Bill:

How to calculate the Percentage Increase or Decrease of a $ value.
Example -
Site Spend for 01-01-2008 thru 07-31-08 was $ 3,465,660
Site Spend, 2009 YTD as of 07-31-09, was $ 1,673,405
Site Spend down what % between these two amounts ?

Bill,

If some value changes over time then the percentage change is the change as a percentage of the original value. That is

In your case the change is new value - original value = $1,673,405 - $3,465,660 = - $1,792,255. Hence the percentage change is ( - $1,792,255/$3,465,660) × 100 = -51.7%. Since this value is negative there has been a decrease so you might say there has been a 51.7% decrease.

I hope this helps,
Penny

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