Islam Grows, Christianity Slips as Share of World Population, Survey Finds

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.

“It’s just striking that there was such dramatic change in a 10-year period,” said Pew’s Conrad Hackett, the lead author of the report. “During this time, the Muslim and Christian populations grew closer in size. 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.

“Among young adults, for every person around the world who becomes Christian, there are three people who are raised Christian who leave,” Hackett said.

The largest share of Christians — about 31 percent — can be found in sub-Saharan Africa, according to the study. Previously, Europe was home to the largest number of Christians in the world.

“And that’s the result of high fertility, youthfulness and rapid growth in general of sub-Saharan Africa,” Hackett said, “as well as the aging, lower fertility and disaffiliation going on in Europe.”

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