Demographic, economic and financial tensions in Europe are focusing the debate on social security systems on the sustainability and adequacy of benefits guaranteed by those systems to citizens and workers. In some European countries this debate has led the introduction of changes in their social security economic and financial systems.

The reform of public pension system approved in Spain in August 2011 suggests the need to introduce a sustainability factor in order to maintain the ratio of contributions to the system and its expected benefits, through the revision of the basic parameters of the system depending on the evolution of the life expectancy of the population.

This article / presentation analyzes the "generosity" of the Spanish social security system (whose funding scheme is based on a “pay as you go” system) and, in this context; study the most effective mechanisms of automatic adjustments to implement a proper sustainability factor from the actuarial point of view. The evolution of life expectancy is not the unique element to be taken into account for designing such a mechanism, we have to analyze other possibilities, among which we can mention: ratio of contributors / pensioners, dependency ratio, ratio of social security contributions / social security pension expenditures, actuarial present value of future benefits, ratio of actuarial present value of benefits / actuarial present value of contributions, etc. This analysis can provide us improvement conclusions and challenges to achieve for this type of systems in order to ensure the correct coverage of its risks.