Women worldwide had an average of 4.8 children each in 1970. By 2024, that figure had fallen to 2.2, a drop of more than half in just over fifty years and the fastest sustained decline in reproductive behavior ever recorded across the entire human population. The United Nations now counts 131 of 237 countries and territories below the 2.1 replacement threshold, home to roughly two-thirds of the world’s people, a milestone that would have seemed unthinkable at the middle of the 20th century.
This is not one trend but several overlapping ones, unfolding on different timetables in different places. Understanding why families have gotten smaller requires separating the measures, household size, family size and total fertility rate, and separating the causes, because no single explanation accounts for what happened everywhere at once.
What Does a Smaller Family Actually Mean?
Three related but distinct measures get used interchangeably in casual conversation about this topic, and conflating them causes real confusion. Household size counts everyone who lives together, related or not. Family size, in demographic terms, usually refers to the number of children a woman has had, either over her lifetime (completed fertility) or as projected from current birth patterns in a single year (period fertility). The total fertility rate (TFR) is the standard period measure: the average number of children a woman would have if she experienced the current age-specific birth rates throughout her reproductive years.
These measures can move independently. A country’s period TFR can fall sharply in a single decade simply because women are delaying births to later ages, without necessarily producing an equally large drop in the number of children those same women eventually have. That distinction, tempo versus quantum in demographic terminology, matters enormously for interpreting short-term fertility swings.
The Global Shift Toward Smaller Families
UN World Fertility 2024 anchors the historical scale of this shift: global fertility fell from close to 5 births per woman in the 1960s to 3.3 in 1990 and 2.2 in 2024, a decline that has continued almost without interruption for over half a century. Women today have one fewer child, on average, than women did as recently as 1990.
Global Fertility Decline by Decade
| Period | Approx. Global TFR | Change From Prior Period |
|---|---|---|
| 1960s | ~5.0 | baseline |
| 1970 | 4.8 | -0.2 |
| 1990 | 3.3 | -1.5 |
| 2024 | 2.2 | -1.1 |
| 2100 (UN projection, medium variant) | ~1.8 | -0.4 (projected) |
Source: United Nations, World Fertility 2024.
The pace of decline has not been uniform. UN DESA’s World Fertility 2024 report groups countries by when they crossed below the 2.1 replacement threshold: one group, including China, Germany, Japan, Russia and the United States, fell below replacement by 1994 or earlier.
A second group, including Brazil, India, Mexico, the Philippines and Vietnam, crossed the threshold between 1995 and 2024.
A third group, including Bangladesh and Indonesia, is projected to cross it by around 2054. Fertility decline is a single global phenomenon proceeding on three different timelines rather than a single event.
The Main Reasons Families Have Fewer Children
Education and Women’s Life Choices
Rising female educational attainment is one of the most consistently documented correlates of fertility decline across countries and time periods, as more years in school delay entry into marriage and childbearing and expand women’s opportunities outside the home.
Later Marriage and Partnership
As marriage age rises in most parts of the world, the reproductive window available within marriage narrows correspondingly in societies where childbearing remains closely tied to marital status.
Later Parenthood
Delayed first births reduce the number of childbearing years remaining to a woman even if her ultimate desired family size has not changed, contributing to lower period fertility rates independent of any shift in preferences.
Housing and Childcare Costs
In many higher-income countries, the cost of housing large enough for a bigger family, combined with the cost and availability of childcare, is frequently cited by prospective parents as a constraint on family size, though isolating its precise statistical contribution from other economic factors is methodologically difficult.
Employment and Career Timing
Career establishment increasingly competes with the years traditionally used for childbearing, particularly for women, a tension that has intensified as female labor force participation has risen across most regions.
Access to Contraception
Wider availability of effective contraception gives couples more control over the timing and number of births, converting what were once largely biologically determined family sizes into more deliberately chosen ones.
Changing Preferences and Family Norms
Surveyed fertility intentions in many countries have themselves declined over recent decades, suggesting that at least part of the fertility decline reflects genuine changes in how many children people say they want, not only constraints preventing them from having as many as they would otherwise choose.
Lower Child Mortality
As child mortality has fallen worldwide, the historical practice of having more children to offset expected child deaths has become less necessary, a mechanism widely credited as one of the earliest drivers of the fertility transition in now-low-fertility countries.
Why the Pattern Differs Between Countries
The two-thirds of the world’s people who live in below-replacement countries are heavily concentrated in East Asia and Europe, where the transition began earliest. South Korea’s fertility rate, at approximately 0.72 to 0.75 births per woman, is the lowest of any sovereign state, with Hong Kong and Macau recording even lower rates among territories. China’s rate stands near 1.0, and Spain’s near 1.1.
Sub-Saharan Africa remains the clear exception. Niger, Chad and Somalia all have fertility rates near or above 6 births per woman, and Africa is the only major region where fertility remains above the global average and above replacement level. Historically, women in Africa averaged 6 to 7 children as recently as the 1980s, and several countries still approach that level today. This gap means the global fertility transition, while universal in direction, is running roughly two generations behind schedule in the region where it began most recently.
What Smaller Families Mean for Society
A world with fewer children per family is also, mechanically, a world that ages faster. Every country that completes the fertility transition eventually sees its working-age population grow more slowly relative to its retired population, a shift already well advanced in Japan, South Korea and much of Europe and now beginning in China.
Smaller cohorts of children also mean smaller school-age populations over time, altering demand for education infrastructure even as demand for eldercare and pension systems rises. At the household level, smaller families and smaller sibling groups translate directly into the smaller average household sizes documented across household composition data worldwide.
Can Family Size Rise Again?
Family size can, in principle, rise again in any given country, but the global-level evidence for a broad reversal is limited. UN projections put the global TFR at approximately 1.8 births per woman by 2100, continuing the downward trend rather than reversing it, though the UN’s own uncertainty range for that projection is wide, running from 1.6 to 2.2 with less than a 10 percent probability that global fertility exceeds replacement level again by 2100.
A useful distinction here is between desired and achieved fertility. Survey research in numerous countries has found that many people report wanting more children than they end up having, suggesting that at least part of below-replacement fertility reflects unmet reproductive intentions rather than a simple decline in the desire for children. Family policies aimed at reducing the cost of childcare, improving housing affordability for families and supporting parental leave have had, at best, modest and inconsistent effects on national fertility rates in the countries that have tried them most aggressively, and no country that has fallen substantially below replacement level has yet sustained a full return to replacement fertility.
Frequently Asked Questions
1. Why are families getting smaller?
Because of a combination of factors, including rising female education, delayed marriage and childbearing, wider access to contraception, falling child mortality, and changing preferences about ideal family size, none of which fully explains the pattern alone.
2. Does smaller family size always mean population decline?
Not immediately. A country’s population can keep growing for years or decades after its fertility rate falls below replacement, because of demographic momentum from large existing cohorts of young people who have not yet reached childbearing age.
3. Why is fertility falling?
Global fertility fell from about 5 births per woman in the 1960s to 2.2 in 2024, largely because of rising education levels, later marriage and parenthood, contraceptive access, falling child mortality and evolving family size preferences across successive generations.
4. Are people having fewer children by choice?
Partly. Survey evidence suggests fertility intentions themselves have declined in many countries, but there is also a documented gap in several countries between the number of children people say they want and the number they actually have, indicating that constraints, not preferences alone, also play a role.
5. Which country has the lowest fertility rate?
South Korea, at approximately 0.72 to 0.75 births per woman as of the mid-2020s, the lowest among sovereign states, with the territories of Hong Kong and Macau recording even lower rates.
6. Which countries still have large families?
Niger, Chad and Somalia have fertility rates near or above 6 births per woman, among the highest in the world, and Sub-Saharan Africa as a region remains the only part of the world with fertility clearly above replacement level.
7. What is the difference between household size and family size?
Household size counts everyone living at the same address, related or not. Family size typically refers to the number of children a woman has had, either over her lifetime or projected from current birth rates in a single year.
8. When will global fertility fall below replacement level?
Different sources give different estimates depending on methodology, ranging from the late 2030s to the late 2040s, though the exact timing depends on assumptions that carry genuine uncertainty.
9. Can government policy reverse falling fertility?
Family-friendly policies such as childcare subsidies, parental leave and housing support have shown modest and inconsistent effects in the countries that have tried them most aggressively, and no country with fertility substantially below replacement has yet achieved a sustained full recovery to replacement level.
10. How much has global fertility fallen since the 1960s?
By more than half, from roughly 5 births per woman in the 1960s to 2.2 in 2024, according to UN World Fertility 2024, a decline that has continued for more than five decades with only limited reversal in any region.
Sources
- United Nations Department of Economic and Social Affairs, Population Division, World Fertility 2024
- United Nations press briefing, “Declining Fertility, Rising Child Mortality, Surge in International Migration,” Population Division panel, 2025
- Our World in Data, fertility rate and replacement level analysis, based on UN World Population Prospects
- PopulationPyramids.org, Fertility Rate by Country, UN World Population Prospects 2024/2026 data
- American Society for Reproductive Medicine, press materials on global fertility decline, 2025
- Statista, fertility rate by continent, 1950-2050, UN-based projections
- Mappr, mapped country fertility rates, UN World Population Prospects 2024 data compilation
