The human life cycle includes the whole of age-related social positions held by individuals during the course of their lives. In western societies three stages can be distinguished: a first stage of childhood and adolescence, a second stage of adulthood and a third stage when adults are considered old in the society they live in. The central question in this study is: what are the effects of changes in the life cycle on the demographic ageing and the amount of social public expenditures? The empirical data in this study refer to the following countries: Belgium, the Federal Republic of Germany, Denmark, France, the United Kingdom and the Netherlands. Hypothetically: a) a decline of the fertility of the population, that results in an ageing of the population, is the result of changes in the human life cycle; b) an increase in social public expenditures is the result of the demographic ageing and also of changes in the human life cycle. Results: a) From testing the hypotheses, by comparing the data on the past thirty years of the countries in this study, a strongly negative correlation appears between the participation in school-education and fertility. This relation is interpreted via the growing burden by the task of upbringing for the parental family and by a postponement of the beginning of the family stage in the second life stage. The baby boom after the Second World War was mainly caused by a temporarily earlier start of the family stage. Looked at it in the long run the interpretation of the relation between the employment of women and fertility is not always self-evident. There have been fluctuations in the participation of women in the labour force. These did not always result in the theoretically expected effects on fertility. A decline in female employment can even coincide with a fertility decline. b) The demographic ageing has consequences for the social public expenditures in the preconditions created by specific characteristics of the life cycle and the latent function of politics in the welfare state: the redistribution of the yields of the production in society over the stages of the life cycle. A life cycle with a long period of school-education and a long third life stage goes together with an extensive welfare state. People in the second life stage pay taxes and social insurance contributions for the education and benefits of people in the first and third life stages. The socioeconomic transfers between life stages are a comparatively new phenomenon. The transfers of the welfare state are not a substitution for former private transfers of money or care from the second life stage to the first and the third life stage.