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How to Find population growth rate?

The most straightforward way to calculate population growth rate is to divide the absolute change in population by the starting population.

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There is more than one potential answer to this question, depending on if you are working with straight line growth rates or average growth rates over time.

Both growth rate calculations use straightforward formulas, and neither formula makes use of complex math skills.

The simpler of the two calculation formulas is the formula for straight line growth rate. All you need to know is the present population and the previous population. The amount of time that passed between those two dates is irrelevant.

Let's make up some population numbers. Let's say that the population of Townsville is currently 44,000 people. The previous census done 4 years prior shows that the population was 38,000 people. That's an absolute change of 6,000 people.

The formula that you are going to use can be written two different ways.

Way #1:

Growth rate = absolute change/past population

Way #2:

Growth rate = (current population - past population)/past population

The first formula assumes that you already know the difference in the two population numbers. Let's plug our numbers in using the first formula.

Growth rate = 6,000/38,000

Growth rate = .1578

Multiply by 100 to get a percentage. Feel free to round.

Growth rate = 15.8%

Chances are that the population didn't increase at exactly the same rate from year to year in Townsville. Suppose 1980 was 38,000, 1981 was 38,601, 1982 was 40,402, and 1983 was 44,000. That's not steady growth, so a more accurate calculation would use the formula for average growth rates over time. This formula is as follows.

Growth rate = (Present population/previous population)^1/N - 1

N = the number of years between the starting population and the present population.

Growth rate = (44,000/38,000)^1/4 - 1

Growth rate = (1.15789)^.25 - 1

Growth rate = 1.037 - 1

Growth rate = .03733

Growth rate = 3.7%

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