Growth trends quantify the rate of growth over a specified period of time. A growth trend can be measured over any period of time, such as a month, year or decade. Determining the growth trend can help you predict future growth. For example, if you know the growth trend for a county has been 4 percent for the past 10 years, you can use that information to plan for future needs for city services, such as police or schools.

Subtract the size at the end of the specified period from the size at the beginning of the specified period. For example, if you were finding the growth trend for a city for the year and the city had a population of 15,000 at the start of the year and 16,000 at the end of the year, you would subtract 15,000 from 16,000 to get 1,000.

Divide the change in size by the original size to find the growth trend expressed as a decimal. In this example, you would divide 1,000 by 15,000 to get 0.0667.

Multiply the previous step's result by 100 to convert from a rate to a percentage. Finishing this example, you would multiply 0.0667 by 100 to find the growth trend to be 6.67 percent.