In 1970, a woman in Mexico might have expected to have seven children, on average. By 2014, that figure had fallen to around two. As of 2023, it was just 1.6. That means that the population is no longer making enough babies to maintain itself.
Mexico is not alone: countries around the world are witnessing falling fertility rates. Exceptions are few. The Institute for Health Metrics and Evaluation (IHME) at the University of Washington in Seattle estimates that, by 2050, more than three-quarters of countries will be in a comparable situation.
“There has been an absolutely incredible drop in fertility — much faster than anyone had anticipated,” says Jesús Fernández-Villaverde, an economist at the University of Pennsylvania in Philadelphia. “And it is happening in a lot of countries you would have never guessed.”
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The numbers are clear. What’s uncertain is how problematic this global ‘baby bust’ will be, and how nations should respond. In economies that have been built around the prospect of steady population growth, the concern is over future slumps in innovation and productivity, as well as having too few working-age citizens to support a growing number of older people. Researchers warn of ripple effects, from weakened military power and less political influence for countries with lower fertility rates, to fewer investments in green technology. It is imperative that countries address population decline and its impacts now, says Austin Schumacher, a health metrics researcher at the IHME.
Many countries have been trying to take action, and the data suggest that some strategies are helpful — if politically fraught. But to scientists familiar with the data, even the most effective efforts are unlikely to bring a full rebound in fertility rates. That’s why many researchers are recommending a shift in focus from reversal to resilience. They see room for optimism. Even if countries can only slow the decline, that should buy them time to prepare for future demographic shifts. Ultimately, scientists say, fertility rates that are low, but not too low, could have some benefits.
“We’re not not making babies,” says Barbara Katz Rothman, a sociologist at the City University of New York. “The human race is not folding in on itself.”
What the data say
In the mid-twentieth century, the world’s total fertility rate — generally defined as the average number of children a woman would have during her reproductive years — was five. (Nature recognizes that transgender men and non-binary people might become pregnant. We use ‘woman’ and ‘women’ in this story to reflect language used in the field.) Some dubbed this mid-twentieth surge the baby boom. Ecologist Paul Ehrlich and conservation biologist Anne Ehrlich saw it differently, warning in their 1968 book The Population Bomb that overpopulation would lead to famine and environmental devastation. But they failed to anticipate advances in agricultural and health technology that would enable the population to double to eight billion in a little more than five decades.
Humanity’s impact on the environment has intensified, owing to that growth and to increased consumption in many parts of the world. But concerns about overpopulation have flipped. Population growth has been slowing down over the past 50 years, and the average total fertility rate stands at 2.2. In about half of countries, it has fallen below 2.1, the threshold generally needed to maintain a steady population. Small changes in these numbers can have strong effects. A fertility rate of 1.7 could reduce a population to half its original size several generations sooner than a rate of 1.9, for example.
The case of South Korea is under close scrutiny. Its fertility rate fell from 4.5 in 1970 to 0.75 in 2024, and its population peaked at just under 52 million in 2020. That figure is now declining at a pace that is expected to accelerate.
Forecasts for the world vary. The United Nations and the International Institute for Applied Systems Analysis in Laxenburg, Austria, project gentler declines than the IHME does (see, for example, go.nature.com/4mtkj8b). But demographers generally expect that the global population will peak in the next 30 to 60 years and then contract. If it does, that will be the first such decline since the Black Death in the 1300s.
According to the UN, China’s population might already have peaked in around 2022, at 1.4 billion. India’s could do the same in the early 2060s, topping out at 1.7 billion people. And, assuming the most likely immigration scenario, the US Census Bureau predicts that the US population will peak in 2080 at around 370 million. Meanwhile, many of the steepest near-term crashes are anticipated in middle-income countries: Cuba is expected to lose more than 15% of its population by 2050.
Sub-Saharan Africa is the notable exception. By 2100, more than half of the world’s babies are likely to be born there1, despite it having some of the world’s lowest incomes, weakest health-care systems and most fragile food and water supplies. Nigeria’s fertility rate remains above four, and its population is projected to grow by another 76% by 2050, which will make it the world’s third-most-populous country.
Still, fertility-rate trends are hard to predict. Data gaps persist, and many models rely on the expectation that rates will rebound as they’ve done before. And as the Ehrlichs’ failed forecasts show, the past isn’t always indicative of the future. “We are groping in the dark,” says demographer Anne Goujon, programme director for population and just societies at the International Institute for Applied Systems Analysis.
What’s driving the decline?
The factors behind fertility collapse are numerous. They range from expanded access to contraception and education, to shifting norms around relationships and parenting. Debate continues over which factors matter most, and how they vary across regions.
Some drivers reflect positive societal changes. In the United States, data from the US Centers for Disease Control and Prevention show that fertility has declined in part because of fewer unplanned pregnancies and teenage births. A long-term drop in domestic violence might also have contributed. Research in 2018 by Jennifer Barber, a sociologist now at Indiana University in Bloomington, and her colleagues showed that women in violent relationships have children at around twice the rate as do those in non-violent ones.
Globally, access to contraception has helped to decouple sex from reproduction. In Iran, a national family-planning campaign that started in the 1980s contributed to the largest and fastest fall in fertility rates ever recorded: from nearly seven to under two in less than two decades. The country reversed course around 2006, and is once again promoting policies to increase fertility rates.
Young people in wealthy countries are also forming fewer partnerships and having less sex. Alice Evans, a sociologist at King’s College London, has suggested that online entertainment is outcompeting real-world interactions and eroding social confidence. As women worldwide have gained education and career opportunities, many have grown more selective. Women want independence, while many men expect a “servant at home”, says Fernández-Villaverde. “Women are asking, ‘Why would I marry this person?’ A lot of men are undateable. Truly undateable.”
This disconnect fuels trends such as South Korea’s Four Nos feminist movement — in which many young women are rejecting dating, marriage, sex and childbirth — and a similar ‘boy sober’ movement among US women.
Many young people are also pursuing more education so as to gain jobs that might come with high stress and little stability early on. As a result, even people who pair up might postpone having children or have trouble conceiving because they are older. Those who do have kids face pressure to prepare them for the same high-stakes race for university and career, says Matthias Doepke, an economist at the London School of Economics and Political Science. “It’s not like we have withdrawn from parenting. It’s just that we concentrate all this investment, all these hours, on fewer children.”
Rising costs create further pressures. A UN survey of more than 14,000 people in 14 countries found that 39% cited financial limitations as a reason not to have children (see www.unfpa.org/swp2025). In US cities, births have fallen most sharply where housing prices have risen most rapidly (see go.nature.com/4tqqzsg).
Ultra-low fertility rates tend to emerge where these pressures converge, says Doepke. In South Korea, he says, housing is expensive, the parenting culture is intense and the working culture rewards long hours.
Other contributors include declining sperm counts, potentially linked to environmental toxins. Many prospective parents also have growing anxiety about political and environmental instability, as highlighted in the UN survey. It’s not clear which of these many factors are most important in individual countries. But ultimately, low fertility rates “reflect broken systems and broken institutions that prevent people from having the number of children they want”, says Stuart Gietel-Basten, a sociologist at the Hong Kong University of Science and Technology. “That is the real crisis.”
Countering the crash
The fallout will play out differently around the world. Middle-income countries, such as Cuba, Colombia and Turkey, could be the hardest hit, with falling fertility compounded by rising emigration to wealthier nations.
Urban–rural divides will also deepen. As young people leave small towns, infrastructure such as schools, supermarkets and hospitals shuts down — prompting more to move away. Often, it’s older people who remain.
Globally, ageing is the core issue with population decline. In countries that have shrinking fertility rates, the proportion of people aged 65 or older is projected to nearly double, from 17% to 31% in the next 25 years (see go.nature.com/4fspvh5). As life expectancy rises, the demand for physical and fiscal support grows, yet there is a lag in supply. For the majority of countries hoping to break the fertility fall, tools exist. These include financial incentives, such as US President Donald Trump’s proposal to give each newborn baby US$1,000 in an investment fund.
Data show that baby bonuses yield modest results for fertility. Australia brought in a $3,000 bonus in 2004, later increased to $5,000 (see go.nature.com/4mgrwsc). Although the policy led to 7% more births in the short term, it’s unclear whether families had more children overall or just chose to have them earlier in life. And scientists caution that such incentives can undermine gender equity and reproductive rights by prioritizing population growth over personal choice, restricting access to contraception and abortion, and reinforcing conventional gender roles.
More-effective approaches, they say, include generous parental leave and subsidies for childcare and housing. Nordic countries pioneered such investments, including leave for fathers. Those nations saw slower fertility declines than elsewhere in Europe — although decreases persist.
Researchers say more can be done, such as placing a higher value on care work. “Everything about the making of babies — growing them, birthing them, feeding them — is treated as cheap labour,” says Katz Rothman. Countries where fathers take on more childcare tend to have higher fertility rates. One study in Bulgaria, the Czech Republic, Hungary, Poland and Russia linked greater paternal involvement with a higher likelihood that the mother would have a second child and work full-time. Of course, putting a higher value on care work could increase the costs of raising a child.
There is no silver bullet. No policy will restore fertility rates any time soon, researchers say. But even small gains can add up to form a valuable cushion. “Part of the reason progressive policies get a bad rap is because people expect too much from them,” says Fernández-Villaverde. Even a combined 0.2 or 0.3 increase in the fertility rate could slow down declines and give countries time to adapt. And adaptation deserves more attention, says political demographer Jennifer Sciubba, president of the non-profit Population Reference Bureau in Washington DC. “If people aren’t having children for a mix of reasons, we are better off using our time, money and good ideas to support adaptation,” she says.
Adapting to a new reality
Some strategies can achieve both goals. Strengthening the care workforce, for example, could both encourage people to have families and patch gaps in care for older people. But there are also policies that governments could use to stabilize strained state pension and protection programmes, such as by raising the Social Security tax cap in the United States.
Increasing the retirement age, as some countries are doing, is another option. On average, a 70-year-old in 2022 had the same cognitive ability as a 53-year-old had in 2000, according to data from 41 advanced and emerging economies. Older people who stay productive — whether through continuing to work or caring for grandchildren — can also see improvements in their health and experience less loneliness.
Still, such policy changes can provoke backlash. Proposals to increase the retirement age in Russia in 2018 and in France in 2023 sparked protests, for example. “But it doesn’t have to be a matter of compelling people to work late into old age,” says Rebecca Zerzan, senior editor of the UN Population Fund’s State of World Population report, who is based in New York City. In fact, according to research by the multinational investment bank Goldman Sachs, working lives are already lengthening in some countries, even in those that haven’t brought in major pension reforms.
Immigration is another lever. It can match labour shortages in wealthier nations to high birth rates in poorer ones, says Schumacher. Migrants boost tax revenues and innovation, even when they don’t receive the tax benefits or government assistance that they help to fund, says Karen Guzzo, a sociologist at the University of North Carolina at Chapel Hill. South Korea and Japan have relaxed immigration rules and helped to fill some of their workforce gaps. Still, immigration is a politically sensitive issue. In countries that open their borders to spur growth, people often blame migrants for the challenges brought on by population decline. And brain drain can hurt the economies that migrants leave.
Gietel-Basten urges policymakers to consider several dimensions, beyond the obvious ones. “It is much easier to eradicate child poverty than to boost fertility,” he says. Even if certain prosocial policies don’t “magically unlock an additional baby per family”, says Zerzan, “you’re going to have people who are happier, healthier and able to pursue education alongside work. That will help create a world where people have more hope. And if they have more hope, then they might have the number of kids that they want to have.”
Sciubba agrees. The path to helping people thrive, she says, “is the same path that could potentially create the conditions for people to want to have children.”
Researchers say that a smaller population should bring benefits: a society that has fewer people can lessen pressure on the environment and allow for greater investment in each individual. But a stable economy is key. Without it, a fiscal squeeze could worsen environmental damage, weaken support systems and undermine human rights. Still, there’s reason for optimism. “If you invest in health and education, which can boost productivity, then a slightly lower population can actually raise gross domestic product,” says Gietel-Basten.
Today’s population isn’t necessarily the optimal population, he says. “Declining fertility is only a disaster if you don’t adapt.”
This article is reproduced with permission and was first published on August 19, 2025.
