The average number of years which an individual can expect to live in a given society, normally derived from a national life table. Life expectancy is usually given from birth but may apply at any age, and because, in all societies, mortality rates tend to be rather high in the first year of life, life expectancy at birth is usually significantly lower than at 1 year old. Women consistently have a longer life expectancy than men, especially in more economically developed countries where the risks of childbirth are less than those in less developed countries.

The lower life expectancies for less economically developed countries generally reflect high infant mortality rates, but by the age of 70, the years of life remaining to an individual are, globally, very similar. Thus, the strong correlation between GDP per capita and life expectancy becomes weaker as the age of an individual increases.