Christianity is currently the world’s largest religion, making up a third of the world’s population with 2.2 billion adherents. Pew research shows that Islam is the fastest growing religion in the world. The religious group will make up 30 percent of the world’s population by 2050, compared to just 23 percent of the population in 2010. That means the number of Muslims in the world will nearly equal the number of Christians by 2050.

If Islam’s growth spurt continues, Pew data shows, Muslims could outnumber Christians soon after the year 2070.

That’s not to say that the total number of Christians is decreasing; Christianity’s growth rate is just not as fast as Islam’s. While the number of Christians will increase from about 2.1 billion to 2.9 billion by 2050, Muslims will jump from 1.6 billion to 2.8 billion.

This growth has to do with the relatively young age of the Muslim population as well as high fertility rates.