A "comparatively youthful" population with high fertility rates will result in Islam's future expansion, according to Pew Research Center projections.
In 2010, Christians made up 31 percent of the world's population, while Muslims composed 23 percent. By 2050, Pew predicts, the number of Muslims in the world will be equal to that of Christians, and by 2070, if trends continue, Christians will be outnumbered:
By 2050, U.S. Christians are also expected to decline in numbers from 78 to 66 percent. Muslims worldwide are also expected to increase by about twice the rate of Christians, at a rate of 73 percent compared to 35 percent.