Implicit government guarantees and bank risk

We develop a model on bank risk and implicit government guarantees. This model concerns the willingness and capacity of implicit government guarantees. Using the Option Pricing Theory, we derive a mathematical formulation of maximizing the bank's net present value (NPV) with implicit government guarantees. Unlike previous work, both the loan portfolio and the bank's NPV are regarded as a combination of options underlying the risky project. We conduct comparative static analyses and numerical examples to examine how implicit government guarantees and capital control affect bank risk and its asset scale. The main insight of our analysis is that implicit government guarantees have some unintended consequences: (a) Inefficient and excessive risk taking (including bank's asset and overall risk); (b) Inefficient investment if there is no binding capacity constraint. We show that it is mainly due to the bank's excessive reliance on contingent assets. In addition, we demonstrate the ineffectiveness of capital constraint on risk control under certain circumstances. Therefore, we suggest that the gradual withdrawal of implicit government guarantees should be accompanied by multiple combinations of regulatory measures and proper institutional reform to avoid risk surges.