It is widely recognized that experience with cognitive tests can influence estimates of cognitive change. Prior research has estimated experience effects at the level of groups by comparing the performance of a group of participants tested for the second time with the performance of a different group of participants at the same age tested for the first time. This twice-minus-once-tested method was adapted in the current study to derive estimates of test experience at the level of individual participants. Among the major findings were that experience estimates were smaller at older ages, with measures of vocabulary and speed compared to measures of memory, reasoning, and spatial visualization, and with longer intervals between the first and second occasion. Although relations of overall cognitive ability with test experience effects were weak, there were significant correlations among the experience estimates in different cognitive domains. These results imply that at least in adulthood, simple measures of cognitive change likely underestimate maturational influences on cognitive functioning, and to a greater extent in young adults than in older adults.