A percent growth rate (or sometimes referred to as percent change, growth rate, or rate of change) is a useful indicator to look at how much a population is growing or declining in a particular area. It is also useful when comparing the growth or decline of populations in two different areas or regions. But percent growth rate can be used in other studies besides population (such as employment, unemployment, economic factors, etc.). Any number from one time and any number from another time can be put into the calculation to determine growth rate. This article will show you how to easily calculate the growth rate or percent change.
Things You’ll Need:
 calculator or spreadsheet software

1
The rate of change (percent change, growth rate) from one period to another is calculated as follows:
Percent Change = (value at end of period – value at beginning of period)/value at beginning of period * 100 
2
Another way of expressing the equation for growth rate or percent change is:
Percent change = (VpresentVpast)/Vpast*100In this formula,
Vpresent = present or future value
Vpast = past or present value 
3
To further calculate an annual percentage rate of change, divide the percent change arrived at in step two by N.
N represents the number of years between the two values used in step 2. 
4
Example to calculate growth rate or percent change:
A particular city has a population of 800,000 in 1990 and a population of 1,500,000 in 2008. To find the growth rate of the population in this city, do the following:
Growth Rate = (1,500,000 – 800,000)/800,000 * 100
Growth Rate = 87.5 percentAverage Annual Growth Rate = 87.5% / 18 years
Average Annual Growth Rate = 4.86 percent
Read more: How to Calculate Growth Rate or Percent Change  eHow.com http://www.ehow.com/how_4532706_calculategrowthratepercentchange.html#ixzz1CRo95aDb
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