A recent Pew Research Center study has found that Islam is now the world’s fastest growing religion, surpassing Christianity. While Christianity remains the globe’s largest religious group at 2.3 billion, Islam grew from 2010 to 2020 at a rate of 4 times greater than Christianity. During that decade, the number of Christians worldwide grew by 122 million, while Islam grew by 347 million people, bringing its worldwide total to 2 billion people. In fact, Muslims added more believers during that time period than all other non-Muslim religious groups combined.

One factor that impacted the number of Christians worldwide was the rate of disaffiliation. According to Pew, those who are “religiously unaffiliated” received the most growth from “religious switching,” i.e. changing from one religion to another or leaving religion altogether. According to Pew’s analysis, for every 5.5 people that joined the Christian faith, 17.1 left, making a net loss of 11.6. Meanwhile, the number of Muslims grew twice as fast as the rest of the world’s population.

Kazakhstan experienced the highest rate of growth amongst Muslims, expanding by 8 points. The study did note that Kazakhstan is a “Muslim-majority country that tightly restricts religious activity.” Christianity had the greatest decrease in Australia, down 20 points, with Christianity also declining in Canada and the US by 14 points. The only country with significant growth in Christianity was Mozambique, which has grown by 5 points. One third of the world’s Christians reside now in sub-Saharan Africa, making Africa the continent with the largest share of Christians.

Conrad Hackett, a senior demographer at Pew Research Center, described the study’s methodology to Religion News Service. “We look at the demographic characteristics of these groups, their age structure, how many children they’re having, how much education they have, because these demographic characteristics affect the future size of the religious groups,” he said. “Muslims are having children at a greater number than Muslims are dying. Very little of the change in Muslim population size is a result of people becoming Muslim as adults or leaving Islam as adults,” he added. According to Hackett, for every one young adult who becomes a Christian, three more who were raised in the faith leave. While noting that in some countries like China, people may be religiously affiliated without admitting it, Hackett stated he believed the study showed a broader worldwide trend away from faith. “Sometimes we hear rumors of religious revival, and it’s certainly possible that in particular places religion could grow,” he admitted. “But in this careful 10-year study that we’ve done, the broad trend is that in many places people are moving away from religion.”