This paper studies the interaction between capital income taxation and a means‐tested age pension. Our results document that the existence of a social insurance program financed from general revenue puts an upward pressure on the optimal tax rate. We also show that there is a negative relation between taper (benefit‐reduction) and optimal capital income tax rates. The potential welfare gain from optimizing capital taxation in the presence of a universal retirement transfer system is relatively higher. However, when the transfer is substantially means tested, the gain is lower, because the means test effectively operates as a tax on retirement capital.