Why do banks choose to finance with equity?

•U.S. banks hold equity capital significantly beyond the required minimum.•Bank leverage is negatively related to a level of competition and loan portfolio diversification.•High bank leverage is associated with low past liquidity.•In recessions and expansions, roles of the leverage determinants change.•When banks approach minimum capital requirements, market determinants fade.

A majority of U.S. banks between 1973 and 2012 held equity capital significantly beyond the required minimum. We study the risk-return tradeoff in connection with a bank's capital structure, and identify several new significant market factors that drive the level of equity capital in banks. During normal growth periods, bank leverage is negatively related to a level of competition and loan portfolio diversification, while high bank leverage is associated with low past liquidity. During recessions and expansions, the roles of those factors change following distortions in risk-return tradeoff. In distress, when banks approach regulatory capital requirements, market determinants of book leverage lose their significance; however, leverage does not decrease until a bank is within 1% of the minimal capital threshold.