The natural frequency of human prospective memory increases with age.

Autobiographical memory (AM), the recollection of past experiences, and prospective memory (PM), the prospection of future events, are prominent components of subjective life, yet data on the frequencies of their occurrence are limited. Using experience sampling, we quantified the incidence of AM and PM in natural settings among various age groups. Individuals of all ages reported engaging in AM approximately 10% of the time. In contrast, whereas younger subjects recalled PMs as often as they recalled AMs, older subjects experienced PM twice as frequently. AM occurrence was positively correlated with PM occurrence, most strongly among younger individuals. AM and PM durations were also positively correlated and remarkably stable across age groups. Together, these data identify an age-associated shift in the temporal orientation of recollection and quantify the relationship between AM and PM. More broadly, this approach provides a quantitative foundation of AM and PM occurrence, a crucial yet largely unexplored dimension of recollection.