Doubling time

January 1, 0001

I and many others have said many times the only way to get ahead of demographic growth and to reach the whole of a place/people is with a movement - that grows organically, rapidly multiplying. But while “movements are the answer” a single movement may not be.“Doubling time” is incredibly important to understand.

I’m sure you’ve heard it: “If everyone converted just one other person ‘per year’ the whole world could be evangelized in…” Suppose you have a population of 200 million. You are starting with a single church planting catalyst. How many doubles do you need to have all 200 million be Christians? (Leaving aside all the idea that not everyone will come respond.) 

Answer: 29 doubles.

How long would it take? If each double took precisely the same amount of time - for example, a month or a year - then, the answer: 29 months (or years). (Let’s ignore the demographic issue for the moment.)

*But it won’t take the same amount of time. *Doubles are hard: they don’t occur systematically. Later doubles of larger communities take longer. 

Here’s a description of different levels of doubles and what to expect at each level. Briefly: As more and more people come in, the annual growth rate slows. Every generation added leads to a slower pace of reproduction, because apostolic types are a minority, and not everyone added makes a convert (or brings someone else in). As the population grows larger, other trends start to take hold in the church: conversion begins to feel the sting of defections. And, at much larger populations, the church begins to feel the tug of births & deaths as well. All of these sap population growth. The same pattern can be seen in viral adoption of businesses like social media.

How fast must the church grow? A population of 200 million is growing at 1.49% per annum. This means it will double in size in 46 years. (There is an actual population.) The church has to double faster for it to grow more rapidly than the population (the only way it will reach 100%).

Let’s build a scenario. Most movements seem to take 2 to 3 years to get to consistent 4th generation, or about 1,000 members. We’ll hypothesize the first 11 doubles (to 1,024) took 3 years, for an annual growth rate of 232%. In the model below, the speed rate degrades slowly: under 10,000, each doubling is 90% as fast as the one before it; then 80% as fast for populations under 100,000; then 70% as fast for those under 1 million; then 60%; and so on until the population matches the national growth rate.

I know this seems math heavy. I don’t believe it to be an unrealistic model of reality. The Bhojpuri movement is estimated at somewhere around 6 to 10 to 12 million, and it’s been going since the 1980s. That’s about 30 years to reach somewhere at or around double 24, which is “roughly” in line with the chart. Other movements I’m aware of mirror the early stages of this table.

To put it in story form: a movement takes (on average) 3 years to reach 1,000 members. Then, it seems to “take off”: in half a year it doubles, then it doubles again. It’s been doubling all along, but this is when it’s “noticed.” Ironicallyjust when it seems to be speeding up, it’s really slowing down. 

As the speed of growth slows, naturally the time it takes to double in size grows larger. In this model: In “just 8 years”, the population doubled 17 times to 100,000.

Then, 5 *years *to double 3 times to a million.

Then, *about 45 years *to break 10 million.

Then, about 40 years for every doubling after that - in line with the population.

In all, to take the country on this model would require 2 centuries.

After double 24, it’s no longer a “movement” - growth, if faster than the population, is usually only slightly faster, and declining down to the population growth rate. The reason is obvious, and inescapable: by double 28 the church IS the population, and by definition cannot grow faster.

This is a *generous *scenario. If annual growth rates slow earlier, it will obviously take longer.

The lesson here: *movements *grow fast when they are small–so to take a large population quickly, try to start lots of smallish movements. Don’t try to have one movement take 200 million. Instead, the rule should be: disciples make disciples, churches make churches, leaders make leaders - and movements make movements. Rather than having one movement seek 200 million, encourage it to birth 10 movements that each take 20 million (or better yet 200 movements each working on 1 million, which would take more on the order of a generation).

Yes, this is simplistic. There are additional reasons: one movement will naturally run into tons of barriers. You need multiple movements to surmount cultural, linguistic, geographic and all sorts of other barriers. The logic here holds no matter what the population size. Multiple movements offer speed, redundancy, and resilience. Train more movement starters. A single huge movement can easily become a “big empire.” It won’t work that way. Give the movement away. Build DNA that starts new movements who’ve never heard of you or the work you’re doing. He who saves the movement will lose it. He who loses the movement, the same will see the Kingdom come.