A TFR of 2.1 yields a stable population over time. Population will rise in a country with a TFR above 2.1 and fall with a TFR below 2.1. In 2020 Niger had the world’s highest TFR, at 6.89.

As a result India’s population structure, measured by the relative size of different age groups, looks more stable than China’s. China is ageing alarmingly. Its over-65-year-olds will ...