From a new report by Pew Research Center:

The world's Muslim population is expected to increase by about 35% in the next 20 years, rising from 1.6 billion in 2010 to 2.2 billion by 2030, according to new population projections by the Pew Research Center's Forum on Religion & Public Life. Globally, the Muslim population is forecast to grow at about twice the rate of the non-Muslim population over the next two decades.

Read the full report here.