People & places · 3 min read
What is the fastest-growing religion? Read the data correctly
Pew’s 2010–2020 estimates identify Islam as the fastest-growing major religion. Learn the difference between growth, conversions, shares and forecasts.
The answer needs a period and a measure
In Pew Research Center's worldwide comparison of major religious categories from 2010 to 2020, Muslims were the fastest-growing religious population. Pew estimates growth of about 21%, from roughly 1.7 billion to 2.0 billion people. This is a finding about that decade, published in 2025, not a live count for 2026. [1][2]
The wording matters. A headline about growth can refer to percentage change, people added, population share or conversion. Those measures answer different questions, and a result under one measure should not be silently substituted for another.
Percentage growth versus people added
Percentage growth compares the increase with the starting population. Absolute growth counts additional people. Population share compares a group with the entire population. As a simple hypothetical example, a group rising from ten to twenty doubles, while one rising from a hundred to a hundred and twenty adds more people but grows by a smaller percentage.
Pew estimates that the Muslim population increased by 347 million during 2010–2020. Its share of the world's population rose by 1.8 percentage points to 25.6%. Those are two additional measurements of the same decade: people added and change in population share, alongside the approximately 21% population growth rate. [1][2]
Growth is not a conversion rate
Pew distinguishes natural increase, religious switching and migration. Its account attributes Muslim growth largely to age structure and fertility rather than net switching. Migration can change a country's religious composition, but moving across a border does not itself add a person to the worldwide total. [3]
The study also finds that the religiously unaffiliated gained substantially through switching. That category is analytically important, but it is not a single religion with one doctrine. A claim about the fastest-growing religion should explain whether and how nonreligious categories are included. [1]
Publication year is not observation year
The report's 2025 release presents estimates for 2010 and 2020. Its definitions and methods are part of the result. Do not relabel those estimates as a 2026 census merely because a website article is read or updated in 2026. [1]
This article attributes the estimates to Pew's research program. Several pages from that program explain the results, but they are not independent research teams reproducing the same global estimate. Readers should know both the source of the figures and the scope of the comparison.
What the finding does not predict
A historical rate does not guarantee a future rate. If you need a forecast, use a projection that states assumptions about demographic behavior and religious switching. Do not extend a past percentage indefinitely and present the result as a measured future population.
For a reliable summary, always include the group, geography, observation period, metric and source. Here that means Muslim population growth worldwide, among Pew's major categories, during 2010–2020. Those details make the answer more useful than an undated claim that one religion is growing fastest everywhere and by every measure.
Sources & further reading
The numbered links connect claims to the sources below. Sources checked October 13, 2026 by a separate AI fact-checking agent. This is not human or specialist review. Read our editorial approach.
- How the Global Religious Landscape Changed From 2010 to 2020 ↗Pew Research Center · Accessed October 13, 2026
- 3. Muslim population change ↗Pew Research Center · Accessed October 13, 2026
- 1. Factors driving religious change, 2010–2020 ↗Pew Research Center · Accessed October 13, 2026
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