The following is Stephen Cranny’s fourth guest post here at Times & Seasons. Stephen Cranney is a Washington DC-based data scientist and Non-Resident Fellow at Baylor’s Institute for the Studies of Religion. He has produced over 20 peer-reviewed articles and six children
According to conventional wisdom, the Church in the United States and other developed countries can either be described as in a state of stasis or slow, steady growth. I have no reason to doubt this general consensus, and it appears to be supported by findings by Matt Martinich and others that the Church is consistently adding units in the United States. As I’ve noted elsewhere, raw on-the-rolls membership is not the best indicator of Church growth for a variety of reasons, but increases in units is probably a good indicator of substantive growth, and by these measures the Church appears to be doing fine.
However, this superficial reading can be misleading, as it does not take into account “age structure effects” which may hide very real declines in Church growth that are not readily apparent from a surface reading of the numbers. Age structure effects is a very technical subject, but to summarize: the Church in the US may be forming new wards, registering more members on its rolls, and building more temples to meet increasing demand while actually having undergone changes, such as lower birth rates and a net outflow of members, that will lead to the US Church shrinking once the older generations die off.
To use an analogy, China has not had replacement level fertility for decades now; however, their population is still growing, and it is possible that the Church in the US is in a similar situation: we aren’t actually replacing ourselves, but we are still growing because of an artifact of the age structure of the Church. Despite the appearance of growth on the surface, these changes should not be seen as happening down the road later, but rather as changes that have already happened, with the inevitable but delayed consequential declines of the future baked into the population pyramid of today.
More technically, this phenomenon is known as population momentum, and is the reason that many countries’ populations will continue to grow after they stop replacing themselves through having children. Population momentum can perhaps be most easily understood visually. When a country has high growth rates, its population pyramid looks like pyramid A, so there are more 0-4 year olds than 5-9 year olds, and so forth.
Simple intuition might suggest that if a large family society like pyramid A starts only having a “replacement level” number of children (2.1 in most developed countries) then the population will immediately stop growing, since the country is no longer having more children than they need to replace themselves. However, this is not actually the case, as can be seen in pyramid C, which is larger than pyramid A, and is what population A will look like down the road if everybody starts only having the number of children needed to replace themselves.
Again, this is because the older cohorts are larger because of large families that were formed in the past, not due to actual, current above-replacement growth. Had society kept growing at above-replacement growth it would have been even larger because the base itself would have grown. The analogy with these countries raises the question: is the Church pyramid A, C, or D? Is it actually replacing itself in the United States and elsewhere, growth in raw numbers notwithstanding?
If the pyramid “base” is conceptualized as an increase in “children of record,” that is reported in every general conference, then that suggests that the Church as a whole is pyramid C, since the “children of record” numbers have been relatively flat for the past decade. If this is the case in the US, then most if not all of the growth that is fueling the expansion of wards, stakes, and temples in the US is essentially being caused by childbearing that happened in the past, and once these effects pass through the system growth in church units will stagnate, potentially to nothing, and we’ll enter a time period where no new branches, wards, or stakes are being added.
Calculating the exact amount of population momentum and when this freebie growth will end requires a lot of data that is difficult, but not impossible, to obtain (for example, years ago I calculated population momentum effects of various indigenous native language speaking communities for the Census Bureau). However, these numbers are not available for the Latter-day Saint population, and therefore population momentum cannot be calculated directly. However, by making the assumption that Church population momentum approximates the general population momentum in the US as a whole, the effect of momentum on the appearance of Church growth can be cursorily, back-of-the-envelope estimated. There are obviously a lot of assumptions built into this very simple analysis, but I believe the take-away point is valid.
Specifically, according to the UN projections, if the United States fertility and migration rates had immediately changed to replacement level on January 1st, 2019, the US population would grow .5% a year purely due to population momentum. Consequently, the Latter-day Saint community in the United States would also grow at least .5% purely because of population momentum.
Comparing this to the reported Latter-day Saint growth sheds some light on the actual rate of Church growth. Specifically, in 2018 the US Church grew about .6% in terms of the absolute number of members on Church records, and .3% in terms of additional branches and wards.
In other words, it appears that the currently observed level of growth in the US Church is approximately equal to that which the Church would expect to experience from population momentum alone; if the growth in units is assumed to be a more accurate indicator of growth in active, practicing numbers then the Church appears to be actually contracting in the United States, with the population momentum effects hiding the decline. It is worth noting that, as it is likely that the Latter-day Saint population is younger on average due to members’ well-known penchant for larger families, equating Latter-day Saint momentum with the general US population’s momentum is a conservative assumption: it is probably higher and therefore the proportion of Church growth that comes from momentum effects is probably as well.
While these adjustments may present a bleaker, albeit more accurate, picture of Church growth and decline for members, the fact of the matter is that the fundamentals of Church growth are still demographically sound in the long-run. The future of the world is in the global South; six countries alone are projected to account for half of the world population growth between now and the end of the 21st century, and with one exception (Pakistan), the Church is growing fast in all of them. The Church is experiencing growth in areas that are growing, and the Church is struggling in areas whose populations are or will be declining. However, in the meantime, decline and stagnation in the United States and other core countries may be hidden by population momentum effects.
So what does this mean?
First, it is good that the Church does not build in anticipation of future growth, as this could lead a Scientology-esque situation where we overbuild and have massive, empty, unused buildings once the momentum effects die off.
Second, while the Church will probably continue to enjoy strong growth in the developing world for the foreseeable future, the fact is that the Church has been financially blessed to have its population base in one of the few very wealthy countries with a sizable religious population. As momentum effects wear off and if the Church enters a decline in the US, the tithing spigots will turn off. It is for this (and other reasons) that I am less consternated about the Church’s reserve fund than others. Yes, $100 billion seems a bit extravagant for a “rainy day” fund a la the 2008 crash. However, there is a very real chance the Church will undergo gradually increasing, very real financial pressures as the relative number of lucrative US tithing payers who have traditionally subsidized the Church’s operations in developing countries declines.
And finally, most Church members have taken perpetual Church growth as a truism: almost an additional article of faith that is wrapped up in our sense of prophesied destiny, when in fact we may be entering an era in the next couple of decades where additional US temples simply stop being announced in General Conference and wards and stakes generally stop dividing, and tying our sense of mission to perpetual growth may be a problem when that growth from the large families of the past runs out. Yes, I believe that the Church is the stone cut out of the mountain without hands that will roll to fill the earth, but Nephi also prophesied that its numbers would be few, and those who have tied the Latter-day Saint religious experience to the idea of its inevitable, perpetual growth in every country will probably need to readjust their expectations.
 Cranney, Stephen. “Who Is Leaving the Church? Demographic Predictors of Ex-Latter-day Saint Status in the Pew Religious Landscape Survey.” BYU Studies Quarterly 58, no. 1 (2019): 99-108.
 My own calculations (in 2019, this has been on the shelf for a bit) from the UN “momentum” projection. World Population Prospects 2019. https://population.un.org/wpp/DefinitionOfProjectionVariants/.
 Pew Research Center. 2019. “World’s Population is Projected to Nearly Stop Growing By the End of the Century.” https://www.pewresearch.org/fact-tank/2019/06/17/worlds-population-is-projected-to-nearly-stop-growing-by-the-end-of-the-century/.
 1 Nephi 14:12