This article tackles the question of how, on the one hand, the high life expectancy and, on the other, the increasing age of mothers at childbirth will impact the joint lifetime of three and four generations and will develop in future.

To this end, indicators are derived from the official data on mortality and fertility for the mean joint lifetimes of three- and four-generation families. Because of the complicated data available, the investigation will be restricted to the female succession of generations, and here to an observation of the first-born child in each case. The indicators act as model calculations, which is why they serve above all to indicate (future) developments in mean joint lifetimes. The indicators are calculated for the average jointly-spent lifetime of three-generation families for the period from 1990 to 2060, and of four-generation families for the period from 2010 to 2060.

The result of the calculations for Western Germany show an increase in the jointly-spent lifetime of three generations of up to roughly 35 years in 2000, after which that the figure falls continually to a value of roughly 30 years. A similarly developing trend emerges for four generations, but this is delayed by roughly 30 years towards the future, and reaches the highest value around 2030 to 2040, at roughly seven to ten years. For Eastern Germany, with its even younger age of women at childbirth in both the past and in the present, the maximum jointly-spent life years of three generations at the beginning of the observation period (roughly around 1990) is almost 40 years, after which this indicator falls continuously. The indicator of the average jointly-spent years of four-generation families, by contrast, probably reaches a maximum around 2020, with a value of 12 to 14 years. Also after this, one may anticipate a reduction in the joint lifetimes of four-generation families in Eastern Germany. All in all, the trends of the indicators denote that one may not necessarily conclude from the longer life expectancy that the generations will have a longer joint lifetime, nor that the number of four-generation families will increase. Rather, the three-generation family also appears to remain the decisive generational composition of families in this century.