(Christians, mostly sub-Saharan migrants, take part in a Sunday Mass in a cathedral in Rabat, Morocco, in 2019. The largest share of Christians, an analysis found, can be found in sub-Saharan Africa. (Mosa’ab Elshamy/AP)

WP; While Christians remained the world’s largest religious group at the end of the decade that ended in 2020, Christianity’s growth did not keep up with global population increase. But Islam — the world’s fastest-growing major religion — increased its share of the world population, as did the religiously unaffiliated, the Pew Research Center found in a report released Monday.Even as the overall number of Christians — counted as one group, across denominations — continued to climb to 2.3 billion, the religion’s share of the world’s population decreased by 1.8 percentage points to 28.8 percent, a falloff driven in large part by disaffiliation. The Muslim population, on the other hand, increased by 1.8 percentage points to 25.6 percent, according to the report, which examined changes in religious demographics through an analysis of more than 2,700 censuses and surveys. Muslims grew faster than any other major religion.” The report attributed the growth in Islam to a younger Muslim population — with an average age of about 24, as opposed to a global average age among non-Muslims of about 33 as of 2020 — along with higher fertility rates in some areas and lower rates of disaffiliation as compared with other religions, including Christianity. Nearly a quarter of the world’s population did not identify with a religion in 2020 (24.2 percent), as opposed to 23.3 percent in 2010.The world’s biggest unaffiliated population is estimated to be in China: 1.3 billion people, out of 1.4 billion, followed by the United States, with 101 million disaffiliated out of 331.5 million, and Japan, with 73 million out of 126.3 million. Another group that underwent significant a loss in population were Buddhists, the only religion that had fewer members in 2020 (324 million) than in 2010 (343 million); this was due to disaffiliation and a low birth rate. Those who identified as Hindu and Jewish maintained rates steady with the world’s population, the report found. https://www.washingtonpost.com/world/2025/06/09/islam-christianity-global-population-pew-survey/