Median age
The age that splits a population in half: 50% younger, 50% older.
How it is measured
From full age-structure estimates of the population.
Where the number came from
Age structure became a subject in its own right with demographic transition theory, set out by Frank Notestein and others in the 1940s: as a society moves from high birth and death rates to low ones, it passes through a phase where deaths have fallen but births have not, producing a population that is both growing fast and unusually young. Median age is the compact way to say where a country sits on that path. It also underpins the "demographic dividend" argument developed in the 1990s, which held that the decades when a country has many working-age adults and comparatively few dependants are its best chance to grow rich, and that the window closes. The indicator is therefore read forwards as much as backwards: a median age tells you as much about a country’s next thirty years as about its present.
Worked example: Niger at 15.6, India at 28.8, Japan at 49.8
Our 2025 figures span almost the entire possible range: Niger at about 15.6 years, India at roughly 28.8, the United States near 38.5, China at about 40.1 and Japan at roughly 49.8. In Niger, half the population is a child or young teenager, which means the immediate demand is schools and the medium-term challenge is creating jobs faster than young adults arrive; the accompanying fertility rate of about 5.8 says that pipeline is not narrowing yet. Japan at 49.8 has the opposite arithmetic, with a fertility rate near 1.23, a shrinking working-age population and a population growth rate of about minus 0.5 percent a year. India sits in the middle at 28.8 with fertility just under replacement at about 1.94, which is the classic dividend position: the young cohorts are already born, the dependency burden is falling, and the outcome depends on whether they find productive work. Note what the single number hides. China at 40.1 and the United States at 38.5 look almost identical here, but China arrived at that median through an abrupt fertility collapse and the United States partly through migration, so their next thirty years look nothing alike. Read the median as a pointer to the age pyramid, not a substitute for it.
Figures read from our own median age table; each row there carries its observation year and whether it came from a live feed or the frozen archive.
Our data source
UN World Population Prospects 2024, medium variant.
Refresh cadence: UN WPP revisions are biennial; we track the latest revision.
What to watch for
A single summary of a whole age pyramid: two countries with the same median can have very different dependency burdens. Niger (median near 15) and Japan (near 49) bracket the world.
CIA World Factbook equivalent field: "Median age" (frozen at the January 2026 final edition; our figures continue from live sources).