The optimum quantity of debt for an aging Japan: welfare and demographic dynamics

Japan’s government is heavily indebted, and the current net debt tends to increase. This paper uses an extended life-cycle general equilibrium model with endogenous fertility to investigate an optimal size of government debt from two viewpoints: individual welfare and future demographic dynamics. A simulation analysis finds that the level of net government debt, which maximizes per-capita utility, is negative at − 220% of Japan’s gross domestic product (GDP). The results also indicate that the net debt-to-GDP ratio of − 220% produces a considerable per-capita welfare gain; however, compared to the baseline simulation with a debt-to-GDP ratio of 150%, it substantially decreases the total population in the long run.