Abstract We develop a continuous-time model examining agency conflicts among controlling shareholders (managers), minority shareholders, and creditors in corporate investment decisions. The manager’s private benefits encourage overinvestment, while their equity stake and debt overhang lead to underinvestment. We show these offsetting incentive effects can achieve optimal investment timing under certain conditions. Agency costs exhibit U-shaped relationships with private benefits, tax rates, volatility, managerial ownership, and leverage. The model reveals how the interplay among agency conflicts, tax benefits, and bankruptcy costs shapes optimal ownership and capital structure, explaining several documented empirical patterns in corporate finance.