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# How do you calculate population growth?

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Subtracting a past population value from the present population value, and dividing this result by the past population value, yields the population-growth rate. Multiplying the population-growth rate by 100 yields the growth percentage.

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Population growth is a change in population size during a particular time period. In the simplest calculation, growth rate is equal to [P(t2) - P(t1)]/P(t1), where P(t1) is a past population value and P(t2) is the present population. This calculation yields a growth rate for any chosen time range. It is common to express growth rate as a percentage by multiplying the rate by 100. Dividing the percent population growth by the number of years between t1 and t2 gives an annual growth percentage. For example, a population that experiences 10 percent growth in 10 years has a 1 percent annual growth rate.

The population growth calculation is also an excellent tool for predicting future populations, given a known growth rate. In this case P(t2) is a future population, and the unknown variable, and P(t1) is the present population.

Another method of predicting a future population is to find doubling time. Doubling time is the result of dividing 70 by the percent growth. In this calculation 70 is a constant that derives from the natural log of 2.

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## Related Questions

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Calculate population growth rate by dividing the change in population for the time by the initial population and multiplying by 100. The number is expressed as a percentage.

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Average annual 20th century population growth peaked in 1987 at approximately 92.3 million people, but the average annual 20th century growth rate peaked in 1967 at 2.11 percent of the previous year's population. Population growth is generally expressed as a percentage, and any precise numerical figure is merely an estimate.

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Populations grow exponentially when they can maintain a constant growth rate percentage and can leverage the steady increase in population. Exponential growth of various species have been seen throughout Earth's history.