Humanity likely dips below replacement fertility for the first time - study
In 2026, humanity probably fell below the simple replacement fertility level for the first time in history: not enough children are being born in the world to keep the population stable in the long run.
This conclusion was reached by the authors of the study "Terra Incognita: The Economics of a Shrinking World," Jesús Fernández-Villaverde from the University of Pennsylvania and Patrick Norrick from Northwestern University. The paper is dated August 10, 2026. The authors note that, as far as they know, humanity has never experienced such a demographic situation even during wars or pandemics.
This refers to the total fertility rate (TFR)—the average number of children a woman would have over her lifetime at current birth rates. For developed countries, the replacement level is usually estimated at about 2.1 children per woman, but for the world as a whole the authors calculated a higher threshold—about 2.2. The reason is higher child mortality and a different sex ratio at birth in some countries.
According to the UN baseline scenario, the global TFR in 2026 is about 2.23 children per woman, so formally the world is still slightly above the replacement level. However, Fernández-Villaverde and Norrick believe that international statistics are not keeping up with the speed of the recent fall in fertility.
After adjusting the data to account for new birth statistics, they estimate the actual global rate in 2026 at no more than 2.19 children per woman. In particular, the latest data from Egypt, Mexico and the Philippines turned out to be lower than those incorporated into UN projections. The researchers also suggest that birth numbers may be overestimated in some African countries.
At the same time, the authors caution against defining exactly 2026 as the moment of crossing this threshold. The difference between estimates is only a few hundredths of a child per woman, while demographic statistics margin of error can be greater. According to them, the key point is not whether the world crossed this threshold in 2025, 2026, or will do so in 2027, but that the global fertility rate has already virtually matched the replacement level and continues to decline.
Fertility falling sharply in middle-income countries
One of the most surprising findings of the study was that rich nations are no longer the only main driver of this new stage of demographic decline. Fertility is decreasing especially quickly in low- and middle-income countries in Asia and Latin America, and signs of acceleration are also appearing in Africa.
In 2025, the fertility rate in Thailand was estimated at only 0.87 children per woman, in Colombia at 1.01, Iran at 1.35, Brazil at 1.52. In Mexico it stood at about 1.51, and in Tunisia a year earlier at 1.45. The authors emphasize that previously such low rates were associated mainly with the richest economies.
The researchers analyzed data from 236 countries and territories for the period from 1950 to 2023. In 219 out of 236 countries they found a long-term trend of declining fertility, with no current signs of stabilization. The fastest declines were observed, among others, in Thailand, China, Tunisia, Algeria and Iran.
Population peak may come well before the UN forecast
Declining fertility does not mean that the world population will begin to shrink immediately. Due to demographic inertia, the number of people will keep growing for some time: children are now being born to the large generations who themselves were born several decades ago.
However, if the current trend continues, the authors expect the world population to peak at about 9 billion around 2056, after which it will start to decline.
This forecast differs significantly from the UN World Population Prospects 2024 baseline scenario. In it the peak is expected only in 2084 at about 10.29 billion people. Instead, the authors' estimate is closer to the UN's "low" scenario, which projects a peak of about 8.95 billion in 2053.
What this means for the economy
The consequences of this demographic transition go far beyond mere population numbers. Shrinking cohorts of working-age people will mean slower labor force growth, and therefore lower potential GDP growth rates.
At the same time, governments will have to finance pensions, healthcare and service debts while the number of workers and taxpayers shrinks relative to the elderly population. The authors emphasize that the sustainability of public finances depends not only on GDP per capita but also on the total size of the economy from which pension and debt obligations are funded.
Meanwhile, the researchers do not name a single proven cause of the global fertility decline. Among possible factors they consider higher housing costs, labor market conditions, changing social norms, the spread of smartphones and changes in gender roles within families. As a more speculative explanation, the authors point to "modernity" itself: in the current economic model, a third child becomes increasingly costly in terms of time and resources, while the economic consequences for an individual of being childless are shrinking.
Based on: Terra Incognita: The Economics of a Shrinking World
