In 1950, not a single country in the world had a fertility rate below the replacement threshold of roughly 2.1 births per woman. Today, at least 72 to 83 countries do, depending on the source and reference year, representing about half the world’s population. By 2050, more than 130 countries, roughly two-thirds of humanity, are projected to fall below that line. The number 2.1 has quietly become one of the most consequential figures in global demography, yet it is also one of the most widely misunderstood, routinely treated as a hard switch between population growth and population decline when it is nothing of the kind.
What Does the 2.1 Replacement Level Mean?
Replacement-level fertility is the total fertility rate at which a population, on average, exactly replaces itself from one generation to the next, with each set of parents producing enough surviving children to replace themselves. The commonly cited figure of 2.1 births per woman is not an arbitrary round number: it reflects roughly 2.0 children needed to replace two parents, plus a small margin, typically 0.05 to 0.1, to account for children who do not survive to reproductive age themselves and for a slight natural excess of male over female births.
Crucially, this margin varies by country: in nations with higher child and adolescent mortality, the replacement threshold sits meaningfully above 2.1, sometimes closer to 2.3 or higher, while in countries with very low child mortality, it can sit slightly below 2.1.
Which Countries Are Above 2.1?
Fertility above replacement level today is concentrated overwhelmingly in Sub-Saharan Africa, alongside a smaller number of countries in Oceania, the Middle East and parts of South Asia. Niger, Somalia and Chad all recorded fertility rates above 6 births per woman as of 2020 estimates, with Niger’s rate reported as high as 8 in some measurements, making it home to the highest share of its population under 18, at nearly 57 percent, of any country in the world.
Statista’s continental breakdown confirms that Africa is the only major world region with a fertility rate clearly above the global average and above replacement level, alongside Oceania, a status Africa has held for as long as reliable comparative data exist.
Which Countries Are Below 2.1?
The below-replacement group has grown from zero countries in 1950 to a genuinely global cohort spanning every inhabited continent. A Cambridge University Press demography text citing 2020-era data counts at least 72 countries below the 2.1 threshold, including some that might surprise casual observers: Bangladesh (2.0), Sri Lanka (2.0), Vietnam (1.9), El Salvador (1.8) and Brazil (1.6) all sit below replacement alongside the more commonly cited examples of the United States (1.64), the United Kingdom (1.56), Japan (1.34) and Italy (1.24). South Korea anchors the extreme low end at 0.78 in that same dataset, though more recent Statistics Korea releases put the figure even lower, closer to 0.68 to 0.75.
A separate compilation citing a record-high count found 83 countries below replacement as of a recent measurement year, representing about half the world’s population, up from just 6 countries, Czechia, Estonia, Hungary, Japan, Latvia and Ukraine, representing about 5 percent of the world’s population, half a century earlier.
As of 2016, every single European Union country had sub-replacement fertility, ranging from a low of 1.3 in Portugal, Poland, Greece, Spain and Cyprus to a comparatively high 2.0 in France, the only EU country to approach the replacement line in that measurement year.
Countries Below Replacement Level, Selected Examples
| Country | Total Fertility Rate | Note |
|---|---|---|
| South Korea | 0.68-0.78 | Lowest recorded globally |
| Italy | 1.24 | Long-term sub-replacement |
| Japan | 1.34 | Below replacement since the 1970s |
| United Kingdom | 1.56 | Below replacement |
| Brazil | 1.6 | Below replacement despite historically high fertility |
| United States | 1.64 | Below replacement |
| El Salvador | 1.8 | Below replacement |
| Vietnam | 1.9 | Below replacement |
| Bangladesh | 2.0 | Near but below replacement |
| Sri Lanka | 2.0 | Near but below replacement |
| France | 2.0 | Highest in EU, still below replacement |
Source: Cambridge University Press, “Demography and the Making of the Modern World,” 2024, citing 2020-era comparative fertility data.
Why 2.1 Does Not Immediately Mean Population Growth or Decline
This is the single most important corrective in this entire topic. A country’s fertility rate can fall below 2.1 while its population keeps growing for years or even decades, and can rise above 2.1 without producing immediate growth, because of two separate mechanisms working alongside fertility.
The first is demographic momentum: when a country has a young population, the product of previously high fertility, the sheer number of women entering their reproductive years each year can keep total births high even after fertility per woman has fallen, simply because there are more women having children, even at a lower average rate each. This is why countries like Brazil, China and India, all now at or below replacement level, continued growing in population for years after their fertility rates first crossed below 2.1.
The second is migration. A country’s population can keep growing despite sub-replacement fertility if enough people move in from elsewhere, a pattern visible across much of Europe, Canada, Australia and the United States over recent decades. Conversely, high emigration can accelerate decline in a country that would otherwise be roughly stable based on fertility and mortality alone.
Replacement Fertility Is Not Identical Everywhere
The 2.1 figure is a global rule of thumb, not a universal constant. Countries with higher infant and child mortality require a higher fertility rate to achieve the same generational replacement, since a larger share of children born will not survive to have children of their own. This is why some demographic literature uses a range, often cited as 2.1 in low-mortality developed countries and as high as 2.5 to 3.3 in some higher-mortality developing countries, rather than treating 2.1 as fixed everywhere.
Replacement Fertility Versus Population Replacement
A subtle but important distinction: fertility replacement measures whether births are, on average, enough to replace the parent generation. Population replacement, or population stability more broadly, depends on the combined effect of fertility, mortality and migration together.
A country can have fertility exactly at replacement level and still see its population shrink if migration outflows are large enough, or it can have fertility below replacement and still see its population grow if immigration is substantial, as has been the case in several European countries in recent years.
Which Countries May Move Toward or Away From Replacement Level?
Long-run projections diverge sharply by region. UN 2022 population prospects-based projections cited by European analysts show Western Europe’s fertility rate falling from 1.53 in 2021 to 1.44 by 2050 and 1.37 by 2100, with Eastern Europe falling from 1.38 to 1.19 over the same horizon and Central Europe from 1.48 to 1.21, all moving further from replacement rather than toward it.
Some Eastern European countries, including Ukraine, Serbia, North Macedonia and Bosnia and Herzegovina, are projected to fall below 1.0 births per woman by 2100 in these projections, a level with no modern historical precedent for a large national population.
Meanwhile, high-fertility countries, concentrated in Sub-Saharan Africa, are projected to move gradually toward replacement level over coming decades, though from a starting point so far above 2.1 that most will remain above replacement well past mid-century.
What Happens When Fertility Remains Below Replacement?
Sustained sub-replacement fertility produces population ageing as its most immediate and predictable consequence: with fewer children born each year relative to the existing population, the average age of the population rises steadily, shrinking the working-age share relative to the retired share over time.
Where sub-replacement fertility persists for long enough without sufficient offsetting migration, outright population decline follows, a pattern already established in Japan and several Eastern European countries and projected to spread much more broadly, with one analysis projecting declining fertility to affect 97 percent of countries by end of century, driving the world population, per the UN’s 2022 projections, toward a peak of around 10.4 billion in the 2080s before beginning a long-term decline.
Frequently Asked Questions
1. What is the 2.1 replacement rate?
It is the total fertility rate at which a population exactly replaces itself across generations, roughly 2.0 children needed to replace two parents plus a small additional margin to account for children who do not survive to reproductive age and a slight natural excess of male births.
2. Which countries have fertility above 2.1?
Mostly countries in Sub-Saharan Africa and some in Oceania, the Middle East and South Asia; Niger, Somalia and Chad all recorded fertility rates above 6 births per woman as of recent estimates, among the highest in the world.
3. Does fertility below 2.1 mean population decline?
Not immediately. A country’s population can keep growing for years or decades after fertility falls below replacement because of demographic momentum, the effect of a large existing young population still moving through its childbearing years, and because of continued immigration.
4. Why is replacement fertility approximately 2.1?
It reflects roughly two children needed to replace two parents, plus a small additional margin, typically 0.05 to 0.1 in low-mortality countries, to account for children who do not survive to have children of their own and for a slightly higher number of male than female births.
5. Can immigration offset below-replacement fertility?
Yes, and it already does in many countries. Nations across much of Europe, along with Canada, Australia and the United States, have sustained population growth despite sub-replacement fertility largely because of continued net immigration.
6. How many countries are below replacement fertility today?
Estimates range from about 72 to 83 countries depending on the source and reference year, representing roughly half the world’s population, up from zero countries in 1950 and just six countries as recently as the mid-20th century.
7. Which country has the lowest fertility rate in the world?
South Korea, with estimates ranging from about 0.68 to 0.78 births per woman in recent years, the lowest sustained national fertility rate ever recorded.
8. Is replacement fertility the same in every country?
No. Countries with higher child and adolescent mortality require a fertility rate above 2.1, sometimes considerably above it, to achieve the same generational replacement, since a larger share of children born will not survive to reproductive age themselves.
9. How many countries will be below replacement fertility by 2050?
Projections suggest more than 130 countries, representing about two-thirds of the world’s population, will be below the replacement threshold by 2050, continuing the sharp long-term rise from essentially zero countries in 1950.
10. What is the difference between fertility replacement and population replacement?
Fertility replacement measures only whether births per woman are sufficient to replace the parent generation. Population replacement depends on the combined effect of fertility, mortality and migration, meaning a country can have replacement-level fertility and still shrink through emigration, or below-replacement fertility and still grow through immigration.
Sources
- United Nations Department of Economic and Social Affairs, Population Division, PopFacts 2017/3, “The end of high fertility is near”
- Cambridge University Press, “Demography and the Making of the Modern World,” 2024, chapter on the shrinking population
- Statista, “Fertility rate by world continent, 1950-2020, with projections to 2050”
- Yale Global Online/UN-sourced analysis, “Replacement Fertility Declines Worldwide”
- Euronews, coverage of UN World Population Prospects 2022-based European fertility projections to 2100
- Springer/academic demographic literature, comparative analysis of below-replacement and high-fertility country population shares, 2010 baseline
