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Moving away from organized religion appears to be linked to declining birth rates in modern societies, according to new research. By examining decades of population data in Finland, an analysis reveals that a drop in state church membership is associated with the continuing trend of couples having fewer children. The research was published in the journal Social Science Research.
Across many high-income countries, birth rates have dropped to historically low levels in recent years. In Finland, the setting for this specific analysis, the total fertility rate fell by thirty percent between 2010 and 2023. The total fertility rate is a demographic measure that estimates the average number of children a woman would have over her lifetime based on current trends. Decreasing birth rates can alter the economic growth trajectory of a society and lead to an aging population that requires more social resource support relative to the active workforce.
Researchers wanted to understand exactly what social factors are driving this decline throughout the industrialized world. Previous sociological analyses have tied historical drops in birth rates to the process of secularization, which is defined as the gradual distancing of a society from religious institutions and values. Less is known about how religion relates to the sharp fertility declines seen specifically in the last two decades. The rapid pace at which younger generations are abandoning organized religion might be contributing to the equally rapid reduction in first-time parenthood.
Henrik-Alexander Schubert, a demographic researcher at the Max Planck Institute for Demographic Research, led the investigation alongside colleagues Vegard Skirbekk and Jessica Nisén. The team proposed that secularization lowers birth rates through a dual mechanism. First, fewer religious individuals exist in the broader population, and religious individuals tend to have more children than non-religious peers. Second, as the pool of religious partners shrinks, surviving religious individuals are more likely to form partnerships with non-religious individuals or remain single.
The research team suspected that this dynamic lowers the chance of childbearing for the remaining religious individuals in the population. To test this theory, they needed to look at the process of family formation from the perspective of couples, rather than just individuals. They utilized Finland as their testing ground because of its highly secularized culture and its detailed national record-keeping system. While active church attendance in Finland is low, a substantial portion of the population maintains membership in the Evangelical Lutheran state church for cultural or traditional reasons.
To conduct the study, Schubert and his colleagues analyzed Finnish administrative register data covering the period from 1995 to 2019. This massive dataset provided a complete record of the registered population residing in the country. To determine religious affiliation, the researchers looked at church tax payments. In Finland, members of the state church pay a specific tax based on their municipal income, which is collected automatically.
Citizens can formally leave the church by filling out administrative paperwork or utilizing online portals, which exempts them from the tax in the following year. Because maintaining membership involves a financial cost, the researchers viewed paying the tax as an objective measure of institutional religious affiliation. They combined these tax records with birth registries and multigenerational data to track the timing and number of births among the population. The final dataset included annual records of childless couples, both married and cohabiting, to see how different combinations of religious affiliation influenced the transition to parenthood.
To ensure consistency, the team controlled for a variety of demographic variables that are known to influence family planning. They factored in the household income, educational background, and employment status of both partners in the couple. They also accounted for geographic differences, adjusting for whether the couples lived in urban, semi-urban, or rural areas.
The researchers found that birth rates remained measurably higher among state church members than among non-members throughout the entire twenty-four-year study period. The mathematical gap between the two groups also widened over time. While the birth rate of the religiously unaffiliated population dropped sharply to near an average of one child per woman by 2019, the birth rate of the affiliated population dropped at a much slower pace.
When analyzing the data from the perspective of couples, the researchers uncovered a unique dynamic regarding partner choice. The religious affiliation of both the male and female partners independently correlated with an increased likelihood of having a child. Most notably, couples in which both partners were members of the state church had the highest transition rate to first-time parenthood. The combined effect of two affiliated partners was greater than the sum of their individual demographic characteristics.
As secularization progresses across the country, the number of religiously homogeneous couples decreases. Because the pool of available religious partners is smaller, religious individuals increasingly partner with unaffiliated people. These mixed-religion couples have lower birth rates than couples where both partners belong to the church. The researchers suggest this creates a self-reinforcing downward loop where declining religious affiliation not only shrinks the religious population but also suppresses the birth rates of those who do stay affiliated.
To quantify this impact, the team ran a simulation known as a counterfactual model. This statistical method allowed them to estimate what the birth rate would have been if the share of church members in the population had remained exactly as it was in the year 2000. Under this simulated scenario, the authors found that the country’s overall birth rate would have been higher in 2019. The simulation indicated that the loss of church membership accounted for a measurable portion of the decline in couples having their first child over the study period.
To rule out hidden variables, the researchers employed twin fixed effects models, comparing siblings who had different religious affiliations. This technique helps isolate the association between being affiliated with the church and having children from inherited traits or family background. Even when accounting for these family backgrounds, the positive association between church membership and childbearing persisted.
The study design involved a few limitations that restrict the generalizability of the findings. Because the study relied on the Finnish state church tax system to measure affiliation, the researchers excluded migrants, who are often members of other religious denominations not captured by this specific tax. The financial metric also only measures formal institutional affiliation, failing to capture the personal strength of a person’s religious beliefs or their frequency of attending religious services.
Other cultural and financial shifts are driving the modern fertility decline globally, and a lack of religion is only one part of a larger picture. Economic uncertainty, changes in housing markets, shifting personal preferences, and increased relationship instability all play a role in birth rates dropping across Europe and other high-income nations. The researchers point out that their counterfactual simulation showed secularization only directly accounted for a modest percentage of the total decline.
Future research will need to investigate whether this relationship between secularization and partner demographics appears in other countries without state-sponsored church taxes. The researchers note that evaluating the strength of individual religious beliefs could reveal different patterns, especially concerning gender dynamics. In highly secularized nations, women and men might experience the social aspects of religion differently, which could alter how couples make joint decisions about starting families.
The study, “Secularization and low fertility: How declining church membership changes couples’ childbearing,” was authored by Henrik-Alexander Schubert, Vegard Skirbekk, and Jessica Nisén.