While the world’s population is projected to grow 35% in the coming decades, the number of Muslims is expected to increase by 73% – from 1.6 billion in 2010 to 2.8 billion in 2050.
The main reasons for Islam’s growth ultimately involve simple demographics. To begin with, Muslims have more children than members of the seven other major religious groups analyzed in the study.
It comes down to a simple birth vs. death calculation. For example, look at the number of children at typical married couple has in different countries. In general, two people have to 'make' two people in order for the birth and death rates to remain constant. Countries like Germany and Japan have birth rates dramatically less than that.
Meanwhile, on average, each Muslim woman has an average of 3.1 children, significantly above the next-highest group (Christians at 2.7) and the average of all non-Muslims (2.3). Moreover, in all major regions where there is a sizable Muslim population, Muslim fertility exceeds non-Muslim fertility.
It doesn't take much economic, statistical, or mathematical prowess to predict how many 18-year-olds there will be in 15 years. The reason is that you start by counting the three-year-olds.
Tectonic shifts are happening. It's important to recognize them, and to understand the consequences.