As explained earlier, the total fertility rate (TFR) is a projection, for a particular year, of the average number of live births that females aged 15 in that year will have as they go through the age range (that is, 15– 49) in which females are assumed to be physically capable of childbearing. The TFR is computed by using, or more exactly by summing, all of the age-specific fertility rates that prevailed in the year for which the TFR is calculated, but age-specific fertility rates have utility beyond their contribution to the TFR. To be exact, age-specific fertility rates can reveal (1) the relative level of fertility among females at different ages and (2) whether temporal trends in fertility at the various ages are similar to or differ markedly from one another. The insights gleaned from (1) can inform efforts to modify fertility rates by directing attention to the ages that are the source of the largest numbers of births. These insights can be supplemented by the information gleaned from (2), which allows identification of the ages that over time have been experiencing relatively rapid changes in fertility. The fertility of females at a given age will shift by a greater absolute amount, or will shift at a quicker pace, than the fertility of females at another age to the degree that fertility at the former age is affected by the macro-level forces that influence fertility in a society. When that happens— when fertility at certain ages is changing more than fertility at other ages— some ages can be ranked higher in efforts to alter levels of fertility, with the choice based on the relative contribution that each age makes to overall childbearing. For example, an age that produces fewer births than another age and is undergoing a slower decline in fertility than the other age could be assigned a lower priority, because the lower-priority age has less potential, all else being equal, to contribute to an aggregate reduction in future births. The information derived from both (1) and (2), therefore, can aid in formulating measures that may affect the numerical growth of the population.