Degrading Time to Double

Movements are "rapidly multiplying" or exponential. This multiplication means that, at the minimum, they must double on a regular basis. Time to Double is a measure of the speed of any kind of viral fad. The "Rule of 72" is a quick and easy way to figure out how long this doubling will take: divide 72 by the annual growth rate of the movement, and you'll get the time in years.

The challenge a lot of movements and fads face: as the movement grows in size, the speed of doubling degrades.

Reasons for this vary by organization, fad or movement. Generally, it seems to me to harken back to the difference between early adopters and later adopters: early adopters tend to be "sneezers" who spread a fad far and wide, while later adopters are more likely to "use" or "participate" but less likely to spread.

Movements institutionalize. There's more being a church member, less being an evangelist. There's more using an iPhone and less being an iPhone evangelist.

When movements run up against the wall of a language or culture, it's exceptionally hard to cross the cultural boundary, and this is really where time to double drops dramatically.

The bottom line: in most instances, it is easier to start a new movement (send out new movement planters/starters) than it is to rev up the growth of an existing, large movement.

If you find the speed of growth is dropping, you can look at your training programs and see whether people are being trained to share their faith and make disciples. But you have to recognize only a small percentage will actually do this - and that percentage will decline in time. It may be better to look at how your church/movement is sending out new movement starters.


Those who are not optimized for growth have made the choice to surrender a transformative influence in society. At the same time, how big one grows depends on the overall aim. Each level of doubling may require an entirely different strategy than the one previous. Let’s consider the following: 1. Start with 1 person. Just starting is hard enough. 2. Double to 2: you have a compatriot. This first doubling could potentially be the most difficult, since you’re looking for someone that you will work closely with. This is a choice of personal alignment on goals, whereas doubling from 100,000 to 200,000 people is more a growth optimization problem. 3. Double to 4: you have a team. Many small businesses and entrepreneurial startups never grow bigger than this stage. Note how Instagram, for example, kept their team very small; most of the time it was about 4 people. Out of 6 million companies in the United States with employees, over half (3.6 million) had 4 employees or less. 4. Double to 8: you have a larger team. Another million companies max out here (so, out of 6 million, 4.6 million have less than 10 employees). If you are seeking growth beyond this level, then what you’re growing is either (a) manpower for a large company, government, military, etc., or (b) followers or users of your platform. At this point in some countries, you have to split, because people aren’t allowed to congregate in large groups. 5. Double to 16: you have a small group. Most church small groups will be on the order of 10 to 12 people; after that, churches talk about splitting. There’s a reason: A group of 16 is about the maximum according to Dunbar’s Number for a small tribe. The intimacy of friendship and personal relationship is lost when the group is much larger than 12. A lot of small groups top out here, because they never undertake what's necessary to turn group members into group leaders. 6. Double to 32: you have a mother/daughter pair of small groups. With ~30 people, you’re talking about a larger retail firm or a growing church. Many churches in small rural areas will be about this size, or one stage bigger. Or, you could be talking about a network, a club, or an association. Leadership structures become important here, because you have relationships between a pair of groups; you've multiplied into more than one group, and you could do it again--if the first time succeeds. 7. Double to 64: you have a multihouse church. In many rural regions, a church will struggle to get bigger than this due to competition with other churches. This size is the max size for many mission agencies, too. At this point you're probably seeing 2nd or 3rd generation growth. You're starting to think, perhaps, about a building, and what you decide now can limit just how many doubles you can do. 8. Double to 128: you have a church in a school facility? In this range, you’re thinking more about a corporate entity that requires some staff (part-time or full-time) to operate, or else a voluntary grouping of people for which the organization is a platform. 9. Double to 256: you are bigger than the average church in America. Right around the average church size in America (~200). Note: consider the case of Bethlehem Baptist (Piper) which had about 300 people in 1980. After it began focusing on missions, it began to grow, and in 10 years doubled and nearly doubled again. Many churches operate at this level with a bi-vocational pastor. 10. Double to 512: you are a multi-service Sunday. This is about the point where, if you are a single congregation, you might be looking for a new building in order to double again to 1,000. You've "broke the 400 barrier" and may be thinking about what it takes to become a megachurch. The decisions that get you to a megachurch size could limit you from being a movement of 100,000 or more. 11. Double to 1,000: Kevin Kelly’s “1,000 true fans” idea puts most artists aiming for this level: 1,000 clients who each buy $100 worth of product or service from you in a given year is a $100,000 business per year. Most churches at this level have full time staff and multiple pastors (senior, youth, administrative, etc). 12. Double to 2,000: you are now on the megachurch list (over 2,000 members). Many churches never reach this level because the population of their towns doesn’t permit it. Only churches in specific population concentrations can. 13. Double to 4,000: you are in the upper half of the US megachurch list. The church has to be in a fairly large urban area to easily accomplish this. 14. Double to 8,000: you are close to the tip-top of the megachurch list. 15. Double to 16,000: Breaking 10,000 members–many of these churches are outside the United States. Only 23 churches in the USA are bigger than you. 15. Double to 32,000: you are bigger than any church in California except Osteen's Lakewood Church (43,500 members). 17. Double to 64,000: you are the largest church in America. You are also larger than most USA cities, which means you really have to be in a megacity. Some more: 18. Double to 128,000: you are a quasi-denominational network. 19. Double to 256,000: you are a quasi-denominational network. 20. Double to 512,000: you are vying for the title of largest church in the world (if you are a single congregation). 21. Double to 1 million: you have more members than most cities have people. 22. Double to 2 million: larger than many denominations. 23. Double to 4 million: you have more people than half of the states of the United States. 24. Double to 8 million: members, more than 40 of the states of the United States. 25. Double to 16 million members, and would compare to the top 4 states of the USA. 26. Double to 32 million: Only California is bigger. 27. Double: Over 64 million members. What Robert Scoble has called “winning the doubling lottery.” Saddleback went from 0 to 20,000 in ~32 years. Facebook went from 0 to 100 million in 4 years–and then in the next 4 years, it went from 100 million to 1 billion. How fast are you doubling? Are you even measuring your doubling time?

The Rule of 72

The Rule of 72 is a quick, coarse way of measuring the time it takes a population to double. First, you’ll need to figure out the growth rate of your population. This is pretty simple: if you’re calculating for a year, then it’s the newer population divided by the older population (e.g. pop2010/pop2009). If you’re calculating for a longer period of time (say a decade), then it’s (new/old)^(1/time_period). So, for example, for a decade, it would be (new/old)^(1/10). (The ^ symbol is “to the power of”; any decent spreadsheet will do it.)

The Rule of 72 is: divide 72 by the population growth rate to get the number of years to double. If the growth rate is 4%, 72/4=18, so 18 years for the group to double in size. If the doubling rate of the group is significantly faster than the doubling rate of the population, you’ll have a chance to double or quadruple in size in the same time the population does so once. For example, if the time-to-double is one-quarter that of the national population, it’s possible 4 “doubling generations” could be done in the same time the national population adds one. If the national population growth is 2%, you’d need growth of about 8 to 10% on a regular basis to reach those kinds of levels (72/2 = 36 years to double, 72/8 = 9 years to double.)

That sounds difficult, but 10% growth just means each small group of 10 adds one new member per year. That’s really not that remarkable a growth rate. Let’s say you start with a church of 100. At an 8% growth rate, by the end of a decade, you would have a church of 200 (72/8=9 years). Keep that sustained and by the end of 16 years you would have a church of 400 (in generation 2, the 200 doubled to 400). Do another decade and you will reach 800. Another decade to 1,600. So, at an 8% growth rate, in 40 years you have 1,600 people.

Now, let’s reverse-engineer. Let’s say you have 100,000 people, and you want to have them all be in a church in 40 years. What kind of growth rate would you need? It’s a fairly simple equation to run in a spreadsheet: you’d need a sustained 20% growth rate with very few dips over a 40 year period. How can you do that? Have everyone in a church in a small group, and each small group of 10 adds 2 new members every year, without fail. In 40 years, the church will have grown to 100,000 people.

Sounds easy, but in practice it’s not. The larger the organism gets, the harder it is for it to grow. This is why it’s very important, early on, to train, coach, and encourage all of your people to be making disciples and multiplying.


No matter where you are in the world, no matter who you are working among, no matter how many believers you have, it will typically not take more than 17 "doublings" of the Christian population to saturate most districts.20 to 25 doubles would suffice for nearly any province. 32 doubles would see the entire world Christian--even if you are starting with just one person. Early doublings can be easy. Later doublings are hard. The biggest question in terms of when the world will be reached is--how long does it take for a given group to double in size? If it takes a year to double, then you're looking at, minimum, about 20 years to saturate an area (provided you maintain speed). If it takes 20 years to double, then you're looking at 400 years. The longer it takes to double, the more can happen "in the meantime" to prevent the doubling from ever taking place. Speed of doubling is your ally. Anything that slows you down increases the risk it will never happen. doubling