The present paper aims to quantify efficiency properties of flat and earnings-related pay-as-you-go financed social security systems of various institutional designs in order to identify an optimal pension design. Starting from a benchmark economy without social security, we introduce alternative pension systems and compare the costs arising from liquidity constraints as well as distortions of labor supply versus the benefits from insurance provision against income and lifespan uncertainty. Our findings suggest an optimal replacement rate of about 50 % of average earnings. In our model a single-tier earnings-related pension system yields the highest efficiency gains dominating flat benefits as well as two-tier systems of any form. We also show that the negative correlation between pension progressivity and pension generosity of real-world social security systems can be justified on efficiency grounds. Finally, our results indicate a positive impact of means-testing flat benefits against earnings-related benefits within multi-pillar pension systems. Copyright Springer Science+Business Media New York 2013
