On Jan. 19 I did a podcast on the Remaining Task for MissioNexus. One of the questions posed then was the following, which I answered online but I am also answering here for the benefit of all:
In recent years, I've heard that the evangelical church is growing more rapidly than Islam. Your statements seem to discredit that idea. Please elaborate.
Speed of growth is measured in terms of annual growth rate, which is expressed as a percentage. The formula for computing annual growth rate is fairly complicated, so I won't go into it here; a fairly detailed discussion can be found in the Wikipedia article.
The raw numbers for growth are as follows, as of 2017:
- Christianity, measured as "all traditions," numbers 2.4 billion and is presently growing at 1.31% p.a. (see Status of Global Christianity 2017)
- Islam numbers 1.7 billion adherents and is presently growing at 1.93% p.a. (fastest).
- Evangelicals as numbered by the World Christian Database (an ecclesiological definition) number 341 million, growing at 2.12%.
- Evangelicals as measured by Operation World (a more beliefs-oriented definition) number 545.5 million, growing at 2.6%.
In terms of annual growth rate (AGR), Islam is the fastest growing religion in the world. By "fastest" I am comparing it to other global numbers: Christianity as a whole, or Hinduism, or Buddhism, etc.
Evangelicals--a subset of global Christianity--are definitely growing faster than Islam. There are two reasons why this is so:
- Evangelicals are a smaller group, and smaller groups have faster annual growth rates. Let's say you have a family of 2 (a husband and wife). They have twins. In one day, the family has grown 100% - doubled - simply by adding 2 more people. If that same family, a few years later, had another set of twins, they would only have grown 50% - because 2 (twins)vs. 4 (the family size of husband, wife, and the original set of twins) is just 50%. (If a family of 2 had quadruplets, they would have grown by 200%!).
- Evangelicals are growing faster than many strands of Christianity because they not only share the same birth rates (as a rule) but also often have higher conversion rates. Global religious dynamics in any given place are births + immigrants + converts - deaths - emigrants - defectors. Islam doesn't have as high a conversion rate as evangelical Christianity does.
You will find this in other subsets of Christianity, too. The Protestant tradition is growing at 1.64%, the Catholic tradition at 1.08%. The Independent tradition as a whole is growing at 2.21% - faster than Islam - and Asian Independents in particular are growing at 2.94%!.
In all of this, we are measuring "faster" by "who has the highest annual growth rate." There is another way of measuring "faster": "who is adding the most new members per year." This is important because having the highest annual growth rate doesn't automatically equate to being the biggest. Just because Asian Independents have the highest AGR doesn't mean they're going to overtake Islam or the rest of the world in terms of raw numbers.
- Asian Independents number 154 million; growing at 2.94% p.a. means this year they will add 4.5 million new members.
- Islam, by contrast, has 1.7 billion, and at 1.93% per year will add 32.8 million. It is a third as fast (rate-wise) but will add nearly 10x as many people.
"Islam is growing faster than Christianity" but that doesn't mean it will overtake Christianity in size. The turtle might be going twice as fast as the rabbit, but if the turtle is 4x further away from the goal, it won't reach the goal "in time" (unless the rabbit stops to take a nap). While "Evangelicals are growing faster than Islam," but they won't overtake Islam in the future--for exactly the same reason.