Several well-documented factors drive the total fertility rate (TFR) down, including female education, lower infant mortality, urbanization, later marriage, higher income levels, and greater access to contraception. The global TFR has already fallen from around 5 births per woman in the 1960s to 2.2 in 2024, and 55 percent of all countries now sit below the replacement level of 2.1 births per woman. Those countries account for 68 percent of the world’s population.
If you’re working through an exam or textbook question, the answer almost certainly includes one or more of the factors below. Here’s how each one works and how large its effect actually is.
Female Education
Education is one of the strongest and most consistent predictors of lower fertility. Research using China’s compulsory schooling reform as a natural experiment found that each additional year of female education reduced the number of births by 0.24 children per woman. That effect was even larger for women in rural areas, where baseline fertility tends to be higher.
The mechanism is straightforward. More years in school delay the age at which women begin having children, expose them to broader career options, and increase the opportunity cost of leaving the workforce. A National Bureau of Economic Research study estimated that each birth reduces a woman’s lifetime paid employment by about four years, roughly 8 percent of her total working life. The more education a woman has, the more earning potential she gives up per child, which creates a powerful financial incentive to have fewer children.
Lower Infant and Child Mortality
When fewer children die in infancy, parents don’t need to have as many births to reach their desired family size. Demographers call this the “target fertility” model: a couple who wants three surviving children in a setting where half of all children die would need six births. When survival rates improve, the required number of births drops accordingly.
This link between mortality and fertility is central to what’s known as the demographic transition, the historical shift from high birth and death rates to low birth and death rates that every industrialized nation has gone through. In developed countries, replacement-level fertility is about 2.1 births per woman. In countries where infant and child mortality remains high, the number of births needed just to replace the population is significantly higher.
Urbanization
Moving from rural to urban areas consistently lowers fertility, for several overlapping reasons. Urban housing is more expensive, which raises the cost of each additional child. Children contribute less to household production in cities than on farms, removing one traditional economic motivation for large families. Urban residents also tend to have better access to family planning services and are more exposed to social norms that favor smaller families and delayed parenthood.
Research on coastal Ghana found that the urban fertility effect reflects a combination of delayed marriage, higher opportunity costs from education and employment, and easier access to contraception. These factors reinforce each other: a woman who moves to a city for work is more likely to delay marriage, stay in school longer, and encounter modern contraceptive options.
Later Marriage and Delayed Parenthood
Postponing marriage is one of the single largest contributors to falling fertility. A demographic study in northwest Ethiopia found that delaying first marriage to age 18 or later reduced fertility by about 23 to 26 percent compared to women who married before 18. Women who married later had an average of 1.9 children, versus 2.7 for those who married early.
The study decomposed the sources of fertility decline in the region and found that postponement of first marriage contributed the most, accounting for 31.4 percent of the total decline. Delaying childbearing to a later age added another 20.4 percent. Together, these timing shifts explained over half the observed fertility reduction. The proportion of currently married women in the study area dropped from 86 percent in 2008 to 55 percent in 2014, while the share of single women rose from under 3 percent to 30 percent.
Economic Development and Higher Income
Wealthier countries consistently have lower fertility rates. As GDP per capita rises, women tend to delay childbearing into their 30s or even 40s to finish education, build careers, or achieve financial independence. This delay shortens the biological window for having multiple children and reduces completed family size.
The relationship is visible in assisted reproduction data: wealthier countries use more fertility treatments precisely because their populations start families later, when natural fertility has already declined. Countries with lower GDP per capita, by contrast, see higher pregnancy rates from fertility treatments partly because their patients tend to be younger.
Access to Contraception
Widespread availability of modern contraception gives women direct control over the number and timing of births. Contraceptive prevalence is one of the most immediate levers for reducing TFR, particularly in regions where desired family size has already fallen but access to birth control remains limited. When contraception becomes available, actual fertility tends to converge quickly toward the number of children people say they want.
Government Population Policies
Some governments have implemented explicit policies to reduce birth rates. The most extreme example is China’s one-child policy, introduced in response to fears of resource scarcity and overcrowding. While coercive policies can produce rapid fertility declines, they often come with significant social costs, including skewed sex ratios and a rapidly aging population. Most countries that have achieved low fertility did so through the indirect factors listed above rather than through top-down mandates.
How These Factors Work Together
No single factor operates in isolation. Economic development funds better healthcare, which lowers infant mortality. Lower infant mortality reduces the perceived need for large families. Education delays marriage, and delayed marriage shortens the childbearing window. Urbanization concentrates all of these forces: cities offer schools, jobs, clinics, and contraceptive access in one place, while simultaneously raising the cost of housing and childcare.
This is why the demographic transition tends to accelerate once it begins. Each factor reinforces the others, creating a feedback loop that can push TFR well below replacement level. As of 2024, 131 countries and territories have fertility rates below 2.1 births per woman, a threshold that, sustained over time, leads to population decline in the absence of immigration.