We often assume humanity will keep multiplying, but a UN forecast suggests our numbers will likely peak near 10.3 billion in the mid-2080s, then shrink — because women now average about one child fewer than in 1990

For most of living memory, the demographic story ran in one direction: more people, every year, without an end in sight. The latest United Nations projection breaks that assumption. The UN now expects the global population to grow to around 10.3 billion in the mid-2080s, then begin a slow decline.

Growth now appears to have an expiry date, and it may be closer than most people assume.

The forecast comes from World Population Prospects 2024, released by the UN Department of Economic and Social Affairs. It draws on census, survey, registration and other demographic data, and the UN now assigns an 80 percent probability to the global population peaking within this century.

A decade ago, the UN put the odds of the population peaking within this century at roughly 30 percent. The 2024 estimate was around 80 percent. As Li Junhua, the UN Under-Secretary-General for Economic and Social Affairs, put it, “The demographic landscape has evolved greatly in recent years.”

What changed the maths

The short answer is fertility. According to World Population Prospects 2024, “Women today bear one child fewer, on average, than they did around 1990.” That single sentence carries much of the demographic work behind the peak, though mortality, migration and age structure matter too.

The numbers are plain enough. The global fertility rate has fallen to about 2.25 births per woman, down from roughly 3.3 in 1990. The threshold that keeps a population stable over the long run, absent migration, is about 2.1 children per woman, and more than half of all countries now sit below it. A drop of one child per woman sounds modest at the scale of a single family. Compounded across a generation and a planet, it is the difference between endless growth and a turning point.

That shift has not been uniform, and the report is careful about it. Li noted that “in some countries, the birth rate is now even lower than previously anticipated, and we are also seeing slightly faster declines in some high-fertility regions.” Lower-than-expected fertility in some of the world’s largest countries, especially China, along with faster-than-anticipated fertility declines in parts of sub-Saharan Africa, is part of why the projected peak is earlier and lower than before.

What a shrinking world looks like

After the mid-2080s peak, the medium projection has the population easing back to about 10.2 billion by 2100. 

The global total hides sharp regional contrasts. By 2024, 63 countries and areas had already passed their population peak, with combined numbers projected to fall by about 14 percent over the next 30 years. Elsewhere, growth continues. The report counts 126 countries still growing through 2054, among them India, Indonesia, Nigeria, Pakistan and the United States. Much of the near-term increase is locked in by age structure rather than by rising birth rates. The UN attributes about 79 percent of growth through 2054 to the momentum of today’s youthful populations.

The other half of the picture is age. By the late 2070s, the UN expects the number of people aged 65 and over to overtake the number of children under 18. A post-peak world is older, with pressures shifting from feeding and housing a growing young population toward supporting an ageing one.

What stays genuinely uncertain

Of course, a forecast that runs to 2100 carries considerable uncertainty in its long tail, and the demographers say so themselves. A later UN fertility report gives a sense of the uncertainty around the long tail: it estimates a 95 percent probability that global fertility in 2100 will fall somewhere between 1.6 and 2.2 births per woman. That range alone is enough to move the peak’s timing and height.

Other modellers expect the fertility decline to go further and faster. A widely cited 2024 projection from the Institute for Health Metrics and Evaluation estimates that by 2100, about 97 percent of countries will have fertility below replacement. The disagreement is real, and it concerns how fast and how far the trend runs, not whether it is happening.

The forecast does not deliver a clean takeaway. Crowding has not been solved, and the species is not running out of people. It describes a handover, from one set of pressures built on growing numbers to another built on shrinking and ageing ones. Whether that trade reads as good news depends almost entirely on what comes next.