The mustard seed.

How Christianity grew from a handful of followers to about 2.7 billion people, compared with other fast-growing movements. The first three centuries are known only from models, and modern growth from counts.

Reach map Scripture translation Growth

Measured 4Model 1Estimate 1Projection tested 1Finding 1

The first three centuries: members by years since founding

Early Christians (Stark's model)Latter-day Saints (records)

Years since founding on the horizontal axis (Christianity counted from 30 CE, the Latter-day Saints from 6 April 1830). Christianity: Rodney Stark's model, 1,000 members in 40 CE growing 40% a decade (The Rise of Christianity, 1996), not counts. Latter-day Saints: the church's own membership records. On a log scale, a steady growth rate is a straight line.

1,000 to 33.9 million

Christians, 40-350 CE

Stark models 1,000 Christians in 40 CE growing 40% a decade to about 6.3 million by 300 and a majority of the empire by 350.

Model

about 6 million (about 10% of the empire)

Christians around 300 CE

Scholars put Christians at about a tenth of a Roman Empire of about 60 million by around 300 CE.

Estimate

6 to 17.9 million

Latter-day Saints, 1830-2025

From six founding members in 1830 to 17.9 million in 2025, about 43% a decade between 1850 and 1990.

Measured

64 to 267 million by 2080

Stark's 1984 projection of Latter-day Saint growth

Stark projected 64-267 million by 2080. Membership was near his high line in 2010 and near the low line by 2025, as growth slowed from about 5% a year to 1-2%.

Projection tested

558 million to 2.66 billion

Christians worldwide, 1900-2025

Christians grew nearly fivefold in 125 years but held a steady third of the world: 34.5% in 1900, 32.5% in 2025.

Measured

200 million to 2.07 billion

Muslims worldwide, 1900-2025

Muslims grew about tenfold, from about an eighth of the world to about a quarter.

Measured

about 1 million to 704 million

Pentecostals and Charismatics, 1900-2025

The renewal movement grew from under a million to about 700 million, the fastest-growing part of Christianity.

Measured

Is early Christian growth unusual?

A 40%-a-decade rate is high but not unique: a modern movement sustained it for over a century under ordinary conditions.

Finding

← All figures

Muslims worldwide, 1900-2025

GradeMeasured

Value: 200 million to 2.07 billion
Source: CSGC (2023)

The Christian case

Christianity remains the larger of the world's two largest faiths: about 2.66 billion Christians against about 2.07 billion Muslims in 2025, on the Center for the Study of Global Christianity's figures. Islam's faster growth over the past century is usually attributed mainly to demography, younger populations and higher fertility, rather than to conversion.

What the research found

Measured: on the same Center's figures, Muslims numbered 200,301,000 in 1900, 574,379,000 in 1970, 1,309,479,000 in 2000 and 2,070,970,000 in 2025. Against a world population of 1.62 billion in 1900 and 8.19 billion in 2025, that is a rise from about 12.4% of the world to about 25.3%: about tenfold in number and a doubling in share, while the Christian share held steady.

Explore the counterarguments

Islam grew faster than Christianity over the last 125 years, roughly doubling its share of the world. Whatever the causes, this shows that very fast growth on a world scale is not unique to Christianity, and it is part of why the growth of a faith, on its own, does not settle questions of truth.