Islam is the world's fastest growing religion, followed by Christianity.
The number of Muslims is expected to rise to 333 million by 2060.

For decades, Christianity has remained the largest religious group in the world accounting for 31% of the Earth’s 7.3 billion people. Islam follows at second place accounting for 24% of the global population, with the other 45% of the population identifying as none (16%), Hindus (15%), Buddhists (7%), and Unaffiliated and adherent folk religions (7%). Therefore, as of 2015, Christianity and Islam made up for more than half of the global population. The global population is estimated to grow by 32% by the year 2060 with Muslims expected to have grown by 70%, making it the fastest growing religious group. The Pew Research Center estimates that in the second half of 21st century, the number of Muslims will have surpassed the number of Christians.
Rapid Muslim Population Growth
The rapid growth of Muslims in the world is expected to be fueled by natural demographic factors such as a young population and high fertility rates. Muslims are the youngest major religious group in the world with a median age of 24. Their highest concentration is in Africa and the Middle East where the global population growth rate is estimated to be the highest. Unlike in other religious groups where women have an average of two children, Muslim women have a higher fertility rate with an average of three children in their lifetime. These dynamics also hold true for regions with a high distribution of Muslims. In India, for example, the number of Muslims is growing faster than the native Hindu religion and is expected to rise to 333 million by 2060. The only regions identified to receive the smallest composition of Muslims is the Caribbean and Latin America as very few Muslims are allowed in the regions.
Religious switching is a major factor that will contribute to the growth of Muslims by 2060. While religious switching is expected to hinder the growth of Christianity by an estimated 72 million, it is expected to have no negative effects on Muslims since they have strict sanctions regarding religious switching.
Growth of Other Religious Groups
A young population coupled with high fertility rates will proliferate Muslims to account for 32% of the global population by 2060. The number of Christians will grow slightly by only 34%, slightly faster than the global population growth rate but far much slower than Muslims. Other religious groups are projected to account for a smaller percentage of the global population in 2060 than they did in 2015. Although it is projected that these religious groups will grow slightly, they will not keep up with the rising global population.
Hindus will grow slightly by 27% while Jews, who are the smallest religious group, are expected to grow by 15%. Adherents of various folk religions such as African traditional religions, Australian aboriginals, and Chinese folk religions will grow by only 5% with the Unaffiliated increasing with only 3%. The population of Buddhists and other smaller religious groups such as Jains and Taoists is expected to decline by 7% by 2060 due to low fertility rates and increasing aging population in China, Thailand, and Japan where they are concentrated.