As the name suggests, the expectation of life is the length of time (generally measured in years) that an individual can expect to live. It is sometimes referred to as ‘life expectancy’. Expectation of life can either be expressed as a future life expectancy (for example 20 years for someone currently aged 65) or a total life expectancy (for example 85 years for someone currently aged 65).

Period life expectancies are determined based on mortality rates for one particular period. They do not assume any future variation in death rates after that period. By contrast, cohort life expectancies are determined using the projected death statistics for one particular birth cohort and do generally assume future variation (typically reduction) in death rates. Life expectancies at birth are lower than at retirement because the latter exclude the effects of pre-retirement deaths.