Why do banks hold capital in excess of regulatory requirements? A functional approach

This paper provides an explanation for the observation that banks hold on average a capital ratio in excess of regulatory requirements. We use a functional approach to banking based on Diamond and Rajan (2001) to demonstrate that banks can use capital ratios as a strategic tool for renegotiating loans with borrowers. As capital ratios affect the ability of banks to collect loans in a nonmonotonic way, a bank may be forced to exceed capital requirements. Moreover, high capital ratios may also constrain the amount a banker can borrow from investors. Consequently, the size of the banking sector may shrink.