Islam is the world’s fastest-growing religion: 6 figures from the latest data

Between 2010 and 2020, the world’s Muslim population grew by 347 million, reaching 2.0 billion. That increase was larger than the growth of every other religion put together.^[1]

Christians grew too, by 122 million, to 2.3 billion. Christianity remains the largest religion on earth. Islam is the one growing fastest.

The claim has a limit worth stating. The religiously unaffiliated, the group Pew calls “nones”, also grew in this period and now form the third-largest category, after Christians and Muslims.^[1] “Fastest-growing” therefore applies among the world’s religions. Pew’s finding is that Islam gained more people than any of them over those ten years.

In 2020 Muslims made up 25.6 percent of the world’s population, a rise of 1.8 points in ten years.^[1] Christians were 28.8 percent.^[2]

The gap between the world’s two largest religions now stands at a little over three points, and it narrowed across the decade.

These figures count identity. A person who calls himself Muslim in a census or survey is counted as Muslim, whether or not he prays or fasts, so the numbers say how many people belong to the community and nothing about how they practise. The same method is applied to every religion, which keeps the comparison fair.

Islam is associated with the Middle East, but the Middle East and North Africa hold only about a fifth of the world’s Muslims. The four countries with the most Muslims are all in Asia: Indonesia with 239 million, Pakistan with 227 million, India with 213 million and Bangladesh with 151 million.^[3]

The typical Muslim is Asian. That surprises most Western readers, and it shapes everything about where the growth happens.

The spread is old and the sources welcome it. The Quran says that God made humankind into peoples and tribes so that they might know one another, and the Prophet’s farewell sermon, as preserved in the Musnad of Ahmad, declared that an Arab has no superiority over a non-Arab except in piety.^[4] Many scholars grade the report sound. A community that is mostly non-Arab has long been the normal state of Islam.

Pew’s explanation is demographic. Its 2017 analysis found Muslim women averaged 2.9 children, above Christians at 2.6 and non-Muslims overall at 2.2. The median Muslim was 24 years old in 2015, seven years younger than the median non-Muslim.^[5] A young population with more children grows faster, and keeps growing as each generation reaches the age of starting families.

The 2025 report adds a sober qualification: much of the growth reflects overall population growth in the countries where Muslims are concentrated.^[1] Pew’s analysts also expected the fertility gap to narrow over time, because birth rates have been falling in many Muslim-majority countries.^[5] A growth rate that rests on youth belongs to a particular stage of national development, and it is one that other religions share wherever their followers are young and numerous.

In 2025 Pew measured religious switching directly, across 117 countries, among adults aged 18 to 54. Of those raised Muslim, 99 percent still identified as Muslim. Of those raised Christian, 83 percent still identified as Christian, and most who left joined no religion at all. Switching had little net effect on the size of the Muslim population.^[6]

This is the figure Muslims can cite with most confidence. Islam’s growth is also a story of retention: the people born into it stay.

A careful reader will add a caution. Surveys rely on what people say about themselves, and in countries where leaving Islam carries legal or social penalties, some respondents may not answer candidly. The result is a measurement with that limitation, and it should be quoted as one. Because switching had little net effect on the Muslim population, the numbers also give no support to a picture of growth by mass conversion.

Pew’s earlier projections expected Muslims to reach nearly 3 billion by 2060, about 31 percent of humanity, and to overtake Christians as the largest religious group in the second half of this century.^[5] Its 2015 report had already found that the two groups would be nearly equal in size by 2050.^[7]

Treat that as a forecast. Pew has updated its baselines since and has not yet published new projections beyond 2020.^[7] A projection holds only while its assumptions about birth rates, ageing, migration and switching hold, and the narrowing fertility gap is one of those assumptions under strain. The measured decade from 2010 to 2020 ran in the direction the forecast predicted.