The UN projects the world population will reach 9.7 billion by 2050, up from about 8.5 billion today. That is an addition of 1.2 billion people in less than 25 years — roughly the population of India added to the world. But the growth will be extremely uneven.

More than half of the growth will come from just eight countries: DR Congo, Egypt, Ethiopia, India, Nigeria, Pakistan, the Philippines, and Tanzania. Sub-Saharan Africa alone will account for about half of global population growth between now and 2050. Nigeria will nearly double, from 231 million to over 400 million, overtaking the United States as the third most populous country.

Meanwhile, many countries will shrink. Japan, Italy, South Korea, Spain, and most of Eastern Europe will see population decline as deaths outnumber births. China's population is already falling and will drop by about 100 million by 2050. Germany and Japan will lose 5–10% of their population unless immigration fills the gap.

The age structure will shift dramatically. The number of people over 65 will double, from 800 million today to 1.6 billion by 2050. In Japan, 40% of the population will be over 65. This aging will strain pension and healthcare systems, even as the working-age population shrinks in many countries.

These projections assume fertility continues to fall. If African fertility falls faster than expected — as it did in Asia — the 2050 population could be lower. If it falls more slowly, it could be higher. The uncertainty is large: the UN's high and low variants for 2050 differ by about 300 million people. But the direction is clear: the world will be larger, older, and more African.