Two-Point-One: The Fertility Line Most of the World Is Now Below

By the populationclock.org team · Published September 21, 2026 · All figures: UN World Population Prospects 2024, medium variant

What the line actually means

Replacement fertility is the number of children per woman at which a population reproduces itself without migration, once the fact that some children do not survive to adulthood is accounted for. In a country with low child mortality that number works out at roughly 2.1, which is why 2.1 has become the shorthand. It is a convention rather than a constant, and it sits somewhat higher in places where mortality in childhood is still high, a point worth keeping in view when the same line is applied to every country at once.

Measured on that line, 136 of the 237 entries in this dataset are below it in 2026, against 101 at or above. The population under the line comes to about 6.01 billion people, roughly 73% of the world. The countries still above the line hold the remaining 27%, though they account for a larger share of the babies: about 49% of this year’s births happen in them, because a population with high fertility is also a young one.

The majority arrived in a single year

Two thresholds matter here, and they were crossed at different times. A majority of countries fell below replacement around 2018. A majority of people did not follow until 2020, and the gap between those dates is the whole story of the last few decades: the line was crossed first by a great many small and medium countries, and only later by the ones with the weight to move the global figure.

That second threshold was crossed almost entirely by one country. The share of humanity living below replacement went from about 49% to about 68% in a single year, because India crossed the line in 2020 carrying roughly 18% of the world’s population with it. Nothing about global fertility changed sharply that year. One very large country moved a fraction of a birth, and the world tipped over a threshold that had been approaching for a generation.

The same shift shows up in the league table. Of the ten largest countries today, seven are below replacement in 2026. Of those same ten countries in the year 2000, only three were.

This is not a rich-country story

The habit of treating low fertility as a European or East Asian condition is now a decade or two out of date. Europe is the most complete case among the larger regions, with 49 of its 50 entries below the line, but Latin America and the Caribbean is not far behind at 39 of 50, and Asia stands at 31 of 51. Among the countries under the line are Indonesia (2.08), Brazil (1.59), Bangladesh (2.09), Mexico (1.85), Philippines (1.86) and Vietnam (1.86), and most of them got there without the incomes usually cited as the cause.

The speed is the surprising part. China first dipped below the line around 1991 and now records about 1.03 births per woman. India’s rate has more than halved since 1990, from about 4.04 to roughly 1.93 today. The lowest rates in the world are lower than most people expect: Hong Kong at about 0.75 and South Korea at about 0.76 are the two lowest among places with more than a million people, and Macao is lower still. At the other end, Chad records roughly 5.84, which is close to where much of the world sat in living memory. East Asia and South Korea in particular show how far below the line a country can go and stay.

Below the line is not the same as shrinking

This is where the arithmetic catches most readers out. Of the 136 places below replacement today, 77 are still adding people this year, and only 60 have passed their all-time population maximum. Low fertility does not shrink a country on contact.

The reason is demographic momentum. A country that had high fertility twenty years ago has an unusually large cohort now entering its childbearing years, so even a below-replacement rate applied to a very large number of potential parents produces more births than deaths for decades. Across the countries below the line whose peak falls inside this projection, the typical gap between crossing 2.1 and reaching maximum population is around 43 years. India is the clearest example: below the line since 2020 and still not projected to peak until about 2062, at roughly 1.70 billion people, a case set out in full in why India’s population will keep growing until the 2060s.

Momentum runs in both directions, which is why the countries that crossed first are the ones shrinking now. South Korea peaked around 2021 and is projected to fall from about 51.6 million to roughly 22.0 million by 2100. Our ranking of countries past their peak lists every country already on the far side of that turn.

Where the line has not been crossed

The exceptions are concentrated almost entirely in one place: 53 of 58 African entries are at or above replacement, and Africa accounts for about 69% of all the people living in above-replacement countries worldwide. The rest are scattered across parts of Asia, Oceania and a handful of countries elsewhere.

That concentration is why the next several decades of world growth are so geographically narrow, a pattern traced in the African century. It is also temporary on the UN’s own assumptions. Nigeria, at about 4.20 today, is projected to cross below 2.1 around 2078. By 2050 the projection has 169 of the 237 entries under the line, and by 2100 it has 224, leaving 13 above it, of which 12 are African.

What it does to the world total

Weighted by population, the average national fertility rate is about 2.15 in 2026, down from roughly 4.93 in 1970. On this measure the world as a whole slips under 2.1 around 2031 and keeps drifting, to about 1.80 by 2100. This is an average of national rates rather than the UN’s own world fertility figure, which weights by women of childbearing age, so treat it as an indicator of direction rather than a headline number.

The important thing is the lag that follows. On the medium projection the world does not reach its maximum population until around 2084, more than 50 years after the global average crosses the line, ending the century near 10.19 billion people. A world that is below replacement and a world that is shrinking are separated by roughly two generations, which is the subject of when will world population peak.

All figures here come from the UN World Population Prospects 2024 medium variant, processed as described in our methodology, with population read on 1 January of each year and fertility read for the calendar year. Country counts include territories the UN reports separately, which is why the total runs to 237. A projection is a conditional statement about what follows from a set of assumptions, and future fertility is the assumption the whole thing rests on: the medium variant has rates drifting back toward replacement from below over the long run, and nothing in the record of the last fifty years makes that a certainty.