This paper investigates the economy-wide effects of mandating private (employment-related) pensions. It draws on the Australian experience with its Superannuation Guarantee legislation which mandates contributions to private retirement (superannuation) accounts. Our key objective is to quantify the long-run implications of alternative mandatory superannuation contribution rates for household economic decisions over the life cycle, household welfare, and macroeconomic and fiscal aggregates. To that end, we develop a stochastic, overlapping generations (OLG) model with labor choice and endogenous retirement, which distinguishes between (i) ordinary private (liquid) assets and (ii) superannuation (illiquid) assets. The benchmark model is calibrated to the Australian economy, fitted to Australian demographic, household survey and macroeconomic data, and accounting for a detailed representation of Australia’s government policy, including its mandatory superannuation system. The model is then applied to simulate the effects of alternative mandatory superannuation contribution rates, with a specific focus on the counterfactual of a legislated future rate of 12% of gross wages. Based on the model simulations, we show that in the long run, this increased mandate generates larger average household wealth, output and consumption per capita and (rational) household welfare across income distribution.