For example, Canada's natural growth rate is 0.3% while its overall growth rate is 0.9%, due to Canada's open immigration policies. In the U.S., the natural growth rate is 0.6% and overall growth is 0.9%. The growth rate of a country provides demographers and geographers with a good contemporary variable for current growth and for comparison between countries or regions. For most purposes, the overall growth rate is the more frequently utilized.

The growth rate can be used to determine a country or region or even the planet's "doubling time," which tells us how long it will take for a country's current population to double. This length of time is determined by dividing the growth rate into 70. The number 70 comes from the natural log of 2, which is .70.

Given Canada's overall growth of 0.9% in the year 2006, we divide 70 by .9 (from the 0.9%) and yield a value of 77.7 years. Thus, in 2083, if the current rate of growth remains constant, Canada's population will double from its current 33 million to 66 million.

However, if we look at the U.S. Census Bureau's International Data Base Summary Demographic Data for Canada, we see that Canada's overall growth rate is expected to decline to 0.6% by 2025. With a growth rate of 0.6% in 2025, Canada's population would take about 117 years to double (70 / 0.6 = 116.666).

The world's current (overall as well as natural) growth rate is about 1.14%, representing a doubling time of 61 years. We can expect the world's population of 6.5 billion to become 13 billion by 2067 if current growth continues. The world's growth rate peaked in the 1960s at 2% and a doubling time of 35 years.

Most European countries have low growth rates. In the United Kingdom, the rate is 0.2%, in Germany it's 0.0%, and in France, 0.4%. Germany's zero rate of growth includes a natural increase of -0.2%, without immigration, Germany would be shrinking, like the Czech Republic.

The Czech Republic and some other European countries' growth rate is actually negative (on average, women in the Czech Republic give birth to 1.2 children, which is below the number to yield zero population growth, approximately 2.1 children). The Czech Republic's natural growth rate of -0.1 can not be used to determine doubling time because the population is actually shrinking in size.

Many Asian and African countries have high growth rates. Afghanistan has a current growth rate of 4.8%, representing a doubling time of 14.5 years! If Afghanistan's growth rate remained the same (which is very unlikely and the country's projected growth rate for 2025 is a mere 2.3%), then the population of 30 million would become 60 million in 2020, 120 million in 2035, 280 million in 2049, 560 million in 2064, and 1.12 billion in 2078! This is a ridiculous expectation. As you can see, population growth percentages is better utilized for short term projections.

Increased population growth generally represents problems for a country - it means increased need for food, infrastructure, and services. These are expenses that most high-growth countries have little ability to provide today, let alone if population rises dramatically.