Declining Fertility and Population Ageing: A 

New Demographic Transition?

Introduction: A World Growing Older, Not Younger

In most parts of the globe, population is no longer expanding at a high rate. Several countries are instead realizing the lowest levels of fertility and are rapidly ageing. The United Nations reports that the world has reduced to an average of 2.3 births per woman in 2023, and in the next decades, further the birth rate is expected to reduce to lower levels (United Nations, 2024b).

 Meanwhile, the population aged 65 years and older is growing at a greater rate than any other category of age (United Nations, 2024a). These changes have put forth a major question: is it a new demographic transition beyond the classical model?

The decrease in fertility and the ageing of the population is not a single occurrence. They are closely related to the economic, social, gender and urbanization changes. This blog presents the theoretical bases of demographic transition, the trends occurring on the global and the Indian scale and the discussion on whether the present trend is an indicator of the new demographic step.

Understanding the Demographic Transition

Frank Wallace Notestein (1902-1983) was an American demographer and the founding director of the Office of Population Research of Princeton University. He is known to have been the one who came up with the theory of demographic transition, which indicates the reason behind the high and low birth and death rates.

Frank W. Notestein was the first to really lay out the idea of demographic transition. He looked at how, as societies industrialize, both birth rates and death rates drop from high to low. In the classic Demographic Transition Model, countries go through four main stages:

·       High stationary (high fertility and mortality)

·       Early expanding (high fertility, declining mortality)

·       Late expanding (declining fertility)

·       Low stationary (low fertility and mortality) (Population Division, 2024)

https://www.researchgate.net/figure/Model-of-demographic-transition_fig1_351718866

Nevertheless, today the fertility rate in many developed nations is much lower than the replacement rate of 2.1 births per woman. This has contributed to the theory of the Second Demographic Transition theorized by Ron Lesthaeghe and is marked by later marriage, cohabitation, individualism and very low fertility rates (Ron Lesthaeghe, n.d.).

Therefore, the demographic trends of the modern world might not be well explained by the classical four-stage model.

International Trends of Reducing Fertility

Decline in fertility is now almost a universal process. The World Bank notes that over fifty percent of the world is made up of countries whose fertility rate is below replacement rate (World Bank Open Data, 2023).

Japan and South Korea are among the East Asian countries that have some of the lowest fertility rates in the world and in the last few years, South Korea has a lower fertility rate of below 1.0 (OECD, 2023). Other European nations such as Italy and Germany also experience low fertility rates and decline in natural population (Eurostat Demography Data, 2025).

Rapid fertility decline is also being witnessed even in developing countries. According to the National Family Health Survey-5, in India, the Total Fertility Rate (TFR) has decreased to replacement level. This is a drastic change of the high fertility rates of seventies (Ministry of Health and Family Welfare, 2021).

Among determinants of fertility, there are:

·       Education of females and their involvement in work.

·       Urbanization

·       Increase in cost of living and raising children.

·       Access to contraception  (Dr. Natalia Kanem, 2023)

The Age of Population Ageing

The percentage of the aged population is on the rise as the fertility and life span are lowering. According to the reports of the World Health Organization one out of six individuals all over the world will be older than 65 by 2050 (World Health Organization, 2025).

In Japan the ratio of old age dependency is very high with almost 30 percent of the population aged 65 and above Europe is also a high dependency country (United Nations, 2024a). In the meantime, India is in the process of getting old; the proportion of the ageing population will increase twofold by 2050 (United Nations, 2024b).

Ageing in population changes the age structure, which raises the old-age dependency ratio and strains the pension systems, healthcare infrastructure and the labor markets.

Is it a new Demographic Transition?

The classical demographic transition gave a forecast on stabilization at low mortality and fertility. But current very low fertility (under 1.5 in most countries) points to the possibility of transition to a fifth stage; population decline and faster ageing.

Other scholars suggest that a post-transition stage is being experienced that is characterized by:

·       Shrinking workforce

·       Rising median age

·       Negative natural increase

·       Migration as demographic compensation.

The Organisation of Economic Co-Operation and Development (OECD) emphasizes that the slowdown in the economic growth of ageing economies will only be countered by productivity or migration to fill labour deficits (OECD, 2023).

Governments in some countries such as Japan and Germany have designed pro-natalist policies such as child allowances and parental leave incentives. Nevertheless, it has been shown that these policies do not have significant effects of turning ultra-low fertility around (OECD Family Database, 2024).

Contemporary Relevance and Policy Challenges

The falling number of births and growing older present several policy issues:

·       Pension sustainability

·       Growth in healthcare expenditure.

·       Labor shortages

·       Intergenerational inequality

In the case of developing nations such as India, it is a two-fold problem, taking advantage of the population bonus and planning ahead regarding ageing. The National Population Policy (2000) of the Government of India was geared towards the realization of replacement-level fertility.

Migration is becoming more and more accepted as the way to solve the issue of demographic imbalance in the world. International Organization of Migration stresses the importance of controlled migration in solving the problem of workforce deficiency (World Migration Report, 2024).

Demographic transition, therefore, is not only a decline in fertility today, but rather a structural change in age composition and socio-economic systems.

Conclusion

Ageing of the population and a reduction in fertility is one of the most critical demographic changes of the 21 st century. Although the classical Model of Demographic Transition is used to explain the overall trend of high birth and low death rates to low birth and low death rates, it fails to explain the ultra-low fertility and zero to negative population growth rate.

The United Nations, World Bank, WHO and OECD suggest evidence that nations are in a new demographic phase where the labor force is ageing, shrinking and the policy is uncertain. It is still unclear whether this should be considered a new demographic transition, but it is quite evident that it is a stage in the global population geography transformation.

The task that lies ahead is not merely the stabilization of the demographics but the modification of economic, social and policy structures to suit a world where the number of children born is lower than it has ever been and the population is living longer than ever.

References

Dr. Natalia Kanem. (2023). SWP Report 2023 | United Nations Population Fund. https://www.unfpa.org/swp2023

Eurostat Demography Data. (2025). Home—Eurostat. https://ec.europa.eu/eurostat

Ministry of Health and Family Welfare. (2021). National Family Health Survey—5. 7.

OECD. (2023). Fertility rates. OECD. https://www.oecd.org/en/data/indicators/fertility-rates.html

OECD Family Database. (2024). OECD Family Database. OECD. https://www.oecd.org/en/data/datasets/oecd-family-database.html

Population Division. (2024, February 17). Population Division | Population Division. https://www.un.org/development/desa/pd/content/population-division

Ron Lesthaeghe. (n.d.). The Unfolding Story of the Second Demographic Transition—Lesthaeghe—2010—Population and Development Review—Wiley Online Library. Retrieved February 14, 2026, from https://onlinelibrary.wiley.com/doi/10.1111/j.1728-4457.2010.00328.x

United Nations. (2024a, January 17). World Population Ageing 2023: Challenges and opportunities of population ageing in the least developed countries | Population Division. https://www.un.org/development/desa/pd/content/world-population-ageing-2023

United Nations. (2024b, February 14). World Population Prospects. https://population.un.org/wpp/

World Bank Open Data. (2023, March 14). World Bank Open Data. World Bank Open Data. https://data.worldbank.org

World Health Organization. (2025, January 10). Ageing and health. https://www.who.int/news-room/fact-sheets/detail/ageing-and-health

World Migration Report. (2024). Worldmigrationreport.iom.int/wmr-2022-interactive/. https://worldmigrationreport.iom.int/wmr-2022-interactive/