Life expectancy

Life expectancy is a statistical estimate of how many more years, on average, people of a given age would live. Most published figures are period life expectancy: they imagine a group of newborns passing through life while facing the age- and sex-specific death rates of one particular year. A life table turns those death rates into the chance of surviving each year of age. Life expectancy at birth is the headline figure, but it can be calculated from any age, such as 60.

Because it sums up death rates across the whole life span, life expectancy is one of the most widely used indicators of a population's overall health, compared between countries, regions, sexes and income groups. It is very sensitive to deaths in early childhood. Where many infants die, life expectancy at birth is low even though adults who survive childhood often reach old age, so a low figure does not mean most people die at that age.

A period figure is not a forecast for any individual. Cohort life expectancy, which follows people actually born in a given year, is usually higher when death rates are falling. A related measure, healthy life expectancy, counts only the years expected to be lived in good health.