Author Samuel Huntington predicts that Islam will overtake Christianity early in the 21st century. By the year 2025, Islam will have 5% more adherents than will Christianity.
The U.S. Center for World Mission estimated in 1997 that Christianity’s total number of adherents is growing at about 2.3% annually. This is approximately equal to the growth rate of the world’s population. Islam is growing faster: about 2.9% and is thus increasing its market share. At this rate, Islam would surpass Christianity as the world’s main religion by 2023 CE.
Most Christian sources predict that Christianity will retain its numerical lead over Islam beyond the year 2025. For example, futurist John Gary stated in 1997: “In no probable statistical scenario reaching out to the year 2200, does Islam surpass Christianity in absolute number of adherents.”