World Population Day: Understanding Your Place in the Global Age Line-up

Somewhere in the age line-up of all 8 billion people alive today, there is a spot with your name on it.

This week, as the world marks World Population Day on July 11, Al Jazeera analysed the latest figures from the United Nations Population Division to build a tool that finds it.

Enter your date of birth and the interactive tells you what share of the world is younger than you, and what share is older, both as a percentage and as the number of people. You can switch the comparison to a single country and watch your position shift. Also, travel forward in time to see where you will sit decades from now, as populations age around you.

The results can be surprising. A person born on the first day of the year 2000, now in their mid-20s, is already older than more than 44 percent of the world. However, that same person is younger than roughly three-quarters of Japan, the world's oldest large nation, where the typical person is already older than 50.

Try it out yourself:

Fifty years ago, in 1976, the median age of the global population was just under 21 years. That means of the 4.1 billion people on Earth at the time, about half were younger than 21 and half were older. Today the median age is 31, and by 2050 the United Nations projects it will reach 36. The typical human being is steadily getting older.

What is the replacement rate?

The engine of that change is fertility. Demographers measure it using the total fertility rate, the average number of children a woman would have over her lifetime at current birth rates. The figure that matters most is the replacement rate, generally put at about 2.1 births per woman. That is the level at which a generation exactly replaces itself, keeping the population stable over the long run without immigration. The slight margin above two accounts for children who do not survive to adulthood.

The global fertility rate today is about 2.2, barely above replacement and down from approximately five in the 1960s. The United Nations expects it to reach the replacement level around the middle of this century and to keep falling after that. More than half of all countries are already below replacement, including China, the United States, India, Japan and most of Europe.

In practical terms, a fertility rate below replacement means that, over time, each generation is smaller than the one before it. Fewer babies today means fewer working-age adults tomorrow, and a growing share of retirees supported by a shrinking workforce. That is the pressure now facing pension systems, health services and labour markets from Italy to South Korea. It is why population ageing, more than raw numbers, is becoming the defining demographic story of the century.

The world's population has quadrupled over the past 100 years, from 2 billion in 1927 to more than 8 billion today. This growth can largely be attributed to the development of modern medicine and the industrialisation of agriculture, which boosted global food supplies.

While the global population continues to reach new highs, demographic experts have pointed out that the annual growth rate has consistently declined to below 1 percent.

According to estimates by the United Nations Population Division, the world will reach some 9.7 billion people by 2050 before growth stalls and, later this century, begins to reverse. The United Nations expects the global population to peak at about 10.3 billion in the mid-2080s.

Where will most people live by 2050?

Where those people live is shifting too. On the latest United Nations projections, the 10 most populous countries in 2050 will be India, China, Nigeria, the United States, Pakistan, Indonesia, Brazil, the Democratic Republic of the Congo, Ethiopia and Bangladesh. India will remain far ahead, with about 1.7 billion people, while China will have fallen to around 1.3 billion and continue to shrink.

The animation below shows how the world’s population tripled from 2.5 billion people in 1950 to 8 billion in 2022.