The UN “Replacement Migration” report (2000) had high impact in academic and civil society. The approach consisted in the estimation of migration volumes required to mitigate the effects of population decline and ageing. The vast number of migrants needed to keep, population sizes, working-age population and the potential support ratio were highlighted as important challenges and impossible goals. Yet the method does take into consideration the social and dynamic nature of working age and old age conceptions.

This communication introduces the concept of prospective age in replacement migration estimations. Prospective age allows integrating a new paradigm in conceptualizing population ageing, accounting not only for the years since birth ("retrospective age"), but also the years an individual can expect to live (“prospective age”). This approach allows defining dynamic age limits for elderly populations.

In our study, the UN methodology is revisited and updated with the comparison of replacement migration estimations according to conventional and prospective age limits. A European perspective is taken, focusing on the Western European countries considered in the original study (United Kingdom, Germany, France and Italy), to which the cases of Portugal and Spain are added. The calculations are based on a population model based on the EUROSTAT scenarios by 2060 using the cohort component method.

The preliminary results show that the main conclusions of the UN report are still valid, although they are significantly moderated by this approach. Replacement migration is not a remedy for ageing, but the volume of migrant’s necessary to maintain the size of the prospective working age population, and the prospective potential support ratio is significantly lower than in the classic estimates.

The introduction of prospective age in this framework inaugurates a line of research in which estimations of migration inputs can be easily calibrated according to different angles of analysis.