Life expectancy
The number of years a newborn would live if current age-specific mortality rates applied for their whole life.
How it is measured
Computed from mortality tables built on death registration and survey data.
Where the number came from
The life table is one of the oldest pieces of quantitative social science. John Graunt analysed London’s bills of mortality in 1662 and produced the first survival table; Edmond Halley built a cleaner one from Breslau’s parish registers in 1693, explicitly so that annuities could be priced correctly. Life expectancy was therefore an actuarial instrument long before it was a development indicator, and it kept the actuary’s logic: it is the average age at death of a hypothetical cohort that lives its whole life under this year’s mortality rates. Nobody actually lives under this year’s rates forever, which is why the figure is properly called period life expectancy and why it is not a forecast of how long today’s babies will live. During a mortality shock the number drops sharply and then rebounds, as it did worldwide around 2020 and 2021, without anyone’s actual lifespan doing anything so abrupt.
Worked example: the United States and China, thirty years apart in income and one year apart in life
Our 2024 figures put the United States at about 78.9 years and China at about 78.0, a gap of under a year, while the 2025 income figures put American GDP per capita near $90,000 against China’s roughly $13,900, a ratio of about six and a half to one. Money buys a great deal of life expectancy at low income levels and very little at high ones; the curve flattens hard, and above roughly middle-income status the differences are driven by diet, violence, drugs, road deaths and health-system access rather than by national wealth. The other end of our table shows what the steep part of that curve looks like: Nigeria at about 54.6 years against Japan at about 84.0, a gap of nearly thirty years. Almost none of that gap is about how long Nigerian eighty-year-olds live. It is dominated by deaths in the first five years of life, which pull the average down with enormous leverage precisely because they subtract a whole lifetime each. This is the single most useful thing to know about the indicator: a low national life expectancy is usually a statement about child mortality, not about old age.
Figures read from our own life expectancy table; each row there carries its observation year and whether it came from a live feed or the frozen archive.
Our data source
World Bank WDI (SP.DYN.LE00.IN), drawing on UN Population Division estimates.
Refresh cadence: Annual; taken on each rebuild.
What to watch for
A period measure, not a prediction: it assumes today’s death rates never improve. Incomplete death registration in many countries means model-based estimates with real uncertainty.
CIA World Factbook equivalent field: "Life expectancy at birth" (frozen at the January 2026 final edition; our figures continue from live sources).