Short answer
Yes, Islam is the fastest-growing major religion, but the numbers alone prove nothing. The Pew Research Center found that from 2010 to 2020 the number of Muslims grew by 347 million. That is more than all other religions combined. By 2020 Muslims were about a quarter of the world. Most of this growth is by birth, because Muslim populations are young. The Qur'an itself warns that following the crowd can lead a person away from God (﷾). What does need explaining is conversion. Every year some people raised to think badly of Islam read its sources and accept it. They come from many backgrounds. Many make this change after reading about Islam for themselves, even when their families object. For Islam, the proof is the message the Prophet (ﷺ) brought, not the head count.
Full explanation
What the figures show
The Pew Research Center is a research group in the United States. In its 2025 study of the world's religions, it found that Muslims were the fastest-growing religious group from 2010 to 2020. Their number rose by 347 million, more than all other religions combined. It reached about two billion, a quarter of the world. The same study explains why. Muslim populations are young and have more children. People joining or leaving Islam as adults made only a small difference to the total. So the size of the Muslim population is not the argument. Conversion is.
Finds that the number of Muslims grew by 347 million from 2010 to 2020, to about 2 billion, more than all other religions combined, and that Muslims rose to 25.6 per cent of the world's population. Very little of this growth came from people becoming Muslim or leaving Islam as adults; most came from natural increase in a young population. Over the same years Hindus grew by 126 million, Christians by 122 million and Jews by nearly 1 million, while Buddhists fell by 19 million.
Most of the growth was by birth. Over the same years Buddhists fell by 19 million.
Numbers do not decide the truth
The Qur'an does not ask anyone to believe because many others do. It warns that following the common run of people on earth leads away from God (﷾). It says that most of mankind will not believe, however much the Prophet (ﷺ) wished it. If size proved truth, the largest religion would always be right. The Qur'an rejects that way of thinking.
“Wert thou to follow the common run of those on earth, they will lead thee away from the way of Allah. They follow nothing but conjecture: they do nothing but lie.”
“Yet no faith will the greater part of mankind have, however ardently thou dost desire it.”
Birth and choice are different
Conversion is a choice, not a birth. In Britain alone, a 2010 study estimated that about 5,200 people a year were becoming Muslim. Most of the converts it surveyed, 62 per cent, were women. Two thirds of the converts it surveyed met a negative reaction from their families at first. The reasons converts give are set out on the page on why people convert to Islam.
Estimates that between 90,000 and 100,000 people in Britain had become Muslim by 2010, with about 5,200 conversions a year, working from a survey of London mosques. Of the 122 converts who answered its own survey, 62 per cent were women and the average age at conversion was 27.5. Books had helped 96 per cent and Muslim friends 86 per cent on their way to Islam. For at least 45 per cent there was no link between conversion and marriage. Two thirds met a negative reaction from their families at first. Of those, 43 per cent said their families later became positive and 28 per cent said they stayed negative. In its follow-up survey of 32 converts, nine in ten of the women had changed the way they dressed. Its survey covered practising converts only.
A faith that invites examination
The Qur'an tells the Prophet (ﷺ) to invite people to God (﷾) on evidence as clear as sight. It forbids forcing anyone into the faith, because truth stands out clear from error. A convert who studies first and decides later is doing what the Qur'an asks.
“Say thou: "This is my way: I do invite unto Allah,- on evidence clear as the seeing with one's eyes,- I and whoever follows me. Glory to Allah! and never will I join gods with Allah!"”
“Let there be no compulsion in religion: Truth stands out clear from Error: whoever rejects evil and believes in Allah hath grasped the most trustworthy hand-hold, that never breaks. And Allah heareth and knoweth all things.”
Perspectives
What the research shows
Islam grew faster than any other religion from 2010 to 2020. This was mainly because Muslim populations are young and have large families.
The number of Muslims grew by 347 million from 2010 to 2020, more than all other religions combined. It rose to 25.6 per cent of the world's population.
Most of that growth came from natural increase, not from adults changing religion.
The Islamic perspective
The size of the Muslim world is not the proof of Islam, and the Qur'an says so itself. The evidence lies in the message the Prophet (ﷺ) brought. People who examine that message freely and accept it show that it invites testing.
The Qur'an warns against following the majority and says most people will not believe.
The Qur'an calls people to faith on clear evidence and forbids compulsion in religion.
Conversion, unlike growth by birth, is a considered choice, often made against family pressure. People of many backgrounds make it every year.