☪ 7th-century Arabia
Islam
The fastest-growing major religion — driven almost entirely by fertility and youth, not by conversion.
Adherents
2.0bn
Share of world
25.6%
Median age
24
Net from switching
+1m
Where it is actually moving
Switching in and out is nearly balanced worldwide. Growth comes from the youngest median age of any major faith and from high-fertility populations in West Africa, the Sahel and South Asia.
Largest Muslim populations
Indonesia
242m · 87%The world's largest Muslim-majority country also contains Bali, a Hindu island of over 4 million within an 87% Muslim nation.
Pakistan
230m · 96%On current fertility, Pakistan is projected to overtake Indonesia as the country with the world's largest Muslim population before 2050.
India
215m · 15%Pew's landmark India survey found 98% of Indian adults still identify with the religion they were raised in — the lowest switching rate of any large country on Earth.
Bangladesh
157m · 91%The Hindu share has fallen from about 22% at independence in 1971 to under 9%, driven by migration rather than conversion.
Nigeria
116m · 52%Africa's most populous country is split almost exactly down the middle, Muslim north and Christian south, and is projected to hold the world's third-largest Christian population by 2060.
Egypt
102m · 90%Egypt's Coptic Orthodox community is the largest Christian population in the Middle East, roughly 10 million people.
Iran
85.4m · 96%Anonymous online surveys consistently find far lower Shia identification than official figures — one of the widest measured gaps between stated and private religion.
Türkiye
81.6m · 96%Survey work finds self-declared 'deists' and non-believers rising fastest among Turks under 30, from a very low base.
Ethiopia
42.8m · 34%Home to Ethiopian Orthodox Tewahedo, one of the oldest continuous Christian traditions, established in the 4th century.
Saudi Arabia
34.4m · 93%Almost all non-Muslim residents are migrant workers; the Hindu and Christian minorities are among the fastest-growing populations in the Gulf by migration alone.
Russia
18.7m · 13%One of the few countries with net movement *into* religion: Orthodox identification rose from about 31% in 1991 to over 70% after the Soviet collapse.
China
14.1m · 1%China holds the largest unaffiliated population on Earth — roughly 875 million people — alongside one of the fastest-growing Protestant communities.