The Mathematics of Population Increase

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These equations can be used to calculate population growth rates.

The variables used are:

pp (present population) = The population at the beginning of the calculation.
fp (future population) = The population after a certain number of years (yrs).
pct (percentage) = The percentage increase in population per period, usually per year.
(In population studies, this is usually taken to mean births minus deaths.)
yrs (years) = The number of years required to effect a certain growth in population.

These equations are similar to Financial Calculations, except they are simpler because they represent a steady population increase and don't try to take into account "interest accrual" and "payments" as separate variables.

An Example:

The world's population in mid-1993 was 5.5 billion people. At the present growth rate of 1.7%, how long will it take to double the population of the world?

The equation for this case is:

This equation shows that it will take 41 years to double the world's population. If this prediction is borne out, there will be 11 billion people on Earth in 2034.

Another Example:

How many more people join us each day?

The equation for this case is:

For this problem we use 5.5 billion for the population, 1.7% for the annual rate of increase, and 1/365 for the argument of years, since we want the rate of increase per day. The result is over 250,000 new people per day.

Here are the remaining statements of the equation:

When using these equations, be sure to enter percentages as ratios, thus 2% = 0.02.

So, given this fantastic population increase, one might ask "What are they doing about it?" There are two answers to this question: (1) nothing, and (2) We are the "they" in the question. It makes no sense to blame third-world countries for uncontrolled population growth. America has 5% of the world's population but consumes 25% of the world's resources. So, in terms of resources used, each new American born equals five world citizens.

The outcome of the math isn't surprising. What is surprising is the fact that many people think we can solve this problem by conserving resources, recycling and so forth. Conservation programs are worthwhile and should be pursued, but they only treat the symptoms of the disease. Addressing resource issues without also confronting the population explosion is what I call "placebo environmentalism."

Zero Population Growth
International Planned Parenthood Federation
Planned Parenthood Federation of America

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