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

Stark's 1984 projection of Latter-day Saint growth

GradeProjection tested

Value: 64 to 267 million by 2080
Source: Deseret News (2011)

The Christian case

In 1984 Stark projected the future growth of the Latter-day Saints, calling it "a new world faith". His high estimate was that "by the year 2080 there would be 267,452,000 Mormons", and his low estimate 63,939,000. In 2010, reported the Deseret News, "Stark's high estimate had church membership at 15,654,000", and the church had about 14 million, "ten years ahead of Stark's low estimate for 2020". The test shows how hard it is to sustain fast growth for long. Christians can point out that the early church, by contrast, kept growing for nearly three centuries, until by about 300 its members are reckoned at about a tenth of the empire.

What the research found

Projection tested: treating Stark's rates as constant, his low line passes about 10.2 million in 2010 and 15.1 million in 2025, and his high line about 15.65 million in 2010 and 28.8 million in 2025. Actual membership was 14.1 million in 2010 and 17.9 million in 2025. Membership was close to the high line in 2010 and has fallen back towards the low line since, as yearly growth slowed from about 5% to 1-2%. Stark said in 2011: "It's slumping slightly ... But it is still awfully good growth."

Explore the counterarguments

The early church's sustained growth is itself known only from Stark's model, which assumes a constant rate between two estimates; no records show whether it, too, rose and slowed over time. So the comparison cannot show that early Christian growth was steadier than this modern movement's. The test also shows that rapid growth did not persist at the rates needed to keep it on Stark's timetable.