A method of predicting numbers of each animal class present in a beef cow herd with either one or two calving seasons per year is described. Breeding cow classes are defined in terms of successive generations from the existing herd, age of cow, calving interval and type of bull mated. Once cow numbers have been established, numbers of other animal classes including replacement females and animals grown for sale can also be derived. The demographic prediction system is demonstrated by showing the time taken for new generations to replace the existing breed in a cow herd breeding its own replacements. A minimum of 9 years was required to replace 80% of the herd with animals that have less than or equal to 25% of the original breed. Up to 4 more years were required to do this with slower rates of turnover, such as when terminal sire usage is maximized or voluntary culling is minimized.