Sub-replacement fertility
Sub-replacement fertility is a total fertility rate that leads to each new generation being less populous than the older, previous one in a given area. The United Nations Population Division defines sub-replacement fertility as any rate below approximately 2.1 children born per woman of childbearing age, but the threshold can be as high as 3.4 in some developing countries because of higher mortality rates. Taken globally, the total fertility rate at replacement was 2.33 children per woman in 2003. This can be "translated" as 2 children per woman to replace the parents, plus a "third of a child" to make up for the higher probability of males born and mortality prior to the end of a person's fertile life. In 2023, the global average fertility rate was around 2.2 children born per woman.
Replacement-level fertility in terms of the net reproduction rate is exactly one, because the NRR takes both mortality rates and sex ratios at birth into account. As of 2010, about 48% of the world population lives in nations with sub-replacement fertility. Nonetheless most of these countries still have growing populations due to immigration, population momentum and increased life expectancy. This includes most nations of Europe, Canada, Australia, Brazil, Russia, Iran, China, India, the United States and many others. In 2016, all European Union countries had a sub-replacement fertility rate, ranging from a low of 1.3 in Portugal, Poland, Greece, Spain and Cyprus to a high of 2.0 in France.
The countries or areas that have the lowest fertility are in developed parts of East and Southeast Asia: Singapore, Hong Kong and South Korea. Only a few countries have had, for the time being, sufficiently sustained sub-replacement fertility to have population decline, such as Japan, Germany, Lithuania, and Ukraine. As of 2020, the total fertility rate varied from 0.84 in South Korea to 7.0 in Niger.
Causes
Higher education
The fact that more people are going to colleges and universities, and are working to obtain more post-graduate degrees there, along with the soaring costs of education, have contributed greatly to postponing marriage in many cases, and bearing children at all, or fewer numbers of children, and the fact that the number of women getting higher education has increased has contributed to fewer of them getting married younger, if at all. In the US, for example, females make up more than half of all college students, which is a reversal from a few decades back.The relationship between higher education and childbearing varies by country: for example, in Switzerland by age 40, childlessness among women who had completed tertiary education is 40%, while in France it is only 15%. In some countries, childlessness has a longer tradition, and was common even before educational levels increased, but in others, such as Southern European ones, it is a recent phenomenon; for instance in Spain the childlessness rate for women aged 40–44 in 2011 was 21.60%, but historically throughout the 20th century it was around 10%. Not all countries show a relationship between low fertility and education: in Czech Republic, of women born in 1961–1965, low educated women were more likely to be childless than high educated women. In the United States in 2022, women between the ages of 15 and 50 with a graduate or professional degree had the highest birthrate, whereas women between the ages of 15 and 50 with less than a high school graduate had the lowest birthrate among all levels of educational attainment of the mother.
A general trade-off
People are more likely in modern society to invest strongly in the needs of their children, such as offering them the best education, shelter, travel, cultural activities etc. In the past, when child mortality was high, people had more children, but invested less in them. Today, parents usually experience much less doubt about whether the child will live to adulthood, and so are more likely to strongly invest in that child. But strongly investing in each child makes it irrational to have a large numbers of children—this is a "quantity vs. quality trade-off"—with education as the most important such qualitative investment.Economic fluctuation
The growth of wealth and human development are related to sub-replacement fertility, although a sudden drop in living conditions, such as the Great Depression, can also lower fertility.In Eastern European countries, the fall of communism was followed by an economic collapse in many of these countries in the 1990s. Some countries, such as those that experienced violent conflicts in the 1990s, were badly affected. Large numbers of people lost their jobs, and massive unemployment, lack of jobs outside the big cities, and economic uncertainty discourages people from having children. For instance, in Bosnia-Herzegovina, the total fertility rate in 2016 was only 1.28 children born/woman.
Financial challenges such as increased housing prices, concern about job security, cost of raising children have also impact on TFR.
Urbanization
Some consider the increase of urbanization around the world a central cause. In recent times, residents of urban areas tend to have fewer children than people in rural areas. The need for extra labour from children on farms does not apply to urban-dwellers. Cities tend to have higher property prices, making a large family more expensive, especially in those societies where each child is now expected to have their own bedroom, rather than sharing with siblings as was the case until recently. Rural areas also tend to be more conservative, with less contraception and abortion than urban areas.Reduction in child labour
Countries which have a high fertility rate are usually less-developed countries, where families rely on children to help them, with labour such as agricultural work, tending to livestock, or even paid work. In such countries child labour is quite common, with children bringing money home, or directly supporting the family through physical work. By contrast, in high-income nations, child labour is almost universally banned, and it is the parents who are expected to invest extensively into their children.Views on the "ideal" family
Although fertility rates are often discussed in terms of state policies, the deeply entrenched social views on what constitutes an "ideal" family may play a crucial role: if parents do not envision large families in a positive way, it is difficult to "persuade" them to have many children. In this regard, there are major differences between European countries: while 50.23% of women aged 15–39 state that the "ideal" family has 3 or more children in Estonia, and 46.43% say this in Finland; only 11.3% say this in Czech Republic, and 11.39% in Bulgaria.Contraception
Changes in contraception are also an important cause, and one that has seen dramatic changes in the last few generations. Legalization and widespread acceptance of contraception in the developed world is a large factor in decreased fertility levels; however, for instance in a European context where its prevalence has always been very high in the modern era, the fertility rates do not seem to be influenced significantly by availability of contraception.While contraception can reduce the number of unwanted births and contribute to a smaller ideal family size, contraception does not start fertility reductions nor substantially affect their size, with these being attributable to other factors.
Assisted reproductive technology
The availability of assisted reproductive technology may foster delay of childbearing, because many couples think that it can solve any future fertility problems. Its effect on total fertility rate is extremely small but government support for it is beneficial for families.Human Development Index
The Human Development Index is a composite statistic of life expectancy, education, and per capita income indicators, which are used to rank countries into four tiers of human development. A country scores higher HDI when the lifespan is higher, the education level is higher, and the GDP per capita is higher. There is a strong inverse correlation between the HDI and the fertility rate of the population: the higher the HDI, the lower the fertility rate. As of 2016, the countries with the highest fertility rate are Burundi, Mali, Somalia, Uganda, Burkina Faso, Zambia, Malawi, Angola, and Afghanistan; while most high-income countries have sub-replacement fertility rates. This is part of the fertility-income paradox, as these high fertility countries are very poor, and it may seem counter-intuitive for families there to have so many children. The inverse relationship between income and fertility has been termed a demographic-economic "paradox" by the notion that greater means would enable the production of more offspring as suggested by the influential Thomas Malthus.Government policies
Some governments have launched programmes to reduce fertility rates and curb population growth. The People's Republic of China implemented a one-child policy for 35 years ; this was relaxed to a two-child policy in 2016 and relaxed further to a three child policy in 2021.Although today Singapore has a low fertility rate, and the government encourages parents to have more children because birth rates have fallen below the replacement rate, in the 1970s the situation was the opposite: the government wished to slow and reverse the boom in births that started after World War II.