Two-thirds of humanity now lives below replacement

Replacement fertility — about 2.1 births per woman, the rate at which each generation exactly refills the one before it — is demography's most famous line, and the world as a whole still sits above it. Barely. The global average stood at 2.19 births per woman in 2024, down from 4.69 in 1960. Read only the average and the story looks unfinished: humanity still replacing itself, with a little to spare. The average is hiding something.

Count countries instead. In 1960, five countries in the World Bank's ledger sat below replacement. By 1990 there were 53. In 2024 there were 117 out of 215 — a solid majority of the world's nations. Weight them by population and the tilt is starker still: about two-thirds of humanity, some 5.5 billion of 8.1 billion people, now live in a country where births no longer replace the people having them.

The newest arrivals at the threshold are the ones that move the global number. India, for decades the engine of world population growth, slipped below replacement in 2020 and recorded about 1.96 births per woman in 2024. Indonesia and Bangladesh sit almost exactly on the line. Mexico, at 1.89, is already through. These are not the greying rich countries of the usual headlines; they are young, middle-income giants whose sheer momentum will keep them growing for decades even as the arithmetic underneath turns over.

The world's fertility rate has not crossed the replacement line. Two-thirds of the world's people already have.

What holds the world average above the line is, increasingly, one continent. Nigeria still records about 4.4 births per woman, and much of sub-Saharan Africa remains far from replacement. When the global average finally crosses, it will be an African story. Almost everywhere else, the crossing has already happened.