We challenge two central tenets of lifecycle investing: (i) investors should diversify across stocks and bonds and (ii) the young should hold more stocks than the old. An even mix of 50% domestic stocks and 50% international stocks held throughout one’s lifetime vastly outperforms age-based, stock-bond strategies in building wealth, supporting retirement consumption, preserving capital, and generating bequests. These findings are based on a lifecycle model that features dynamic processes for labor earnings, Social Security benefits, and mortality and captures the salient time-series and cross-sectional properties of long-horizon asset class returns. Given the sheer magnitude of US retirement savings, we estimate that Americans could realize trillions of dollars in welfare gains by adopting the all-equity strategy.