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A Theory of Bank Capital


  • Douglas W. Diamond
  • Raghuram G. Rajan


Banks can create liquidity because their deposits are fragile and prone to runs. Increased uncertainty can make deposits excessively fragile in which case there is a role for outside bank capital. Greater bank capital reduces liquidity creation by the bank but enables the bank to survive more often and avoid distress. A more subtle effect is that banks with different amounts of capital extract different amounts of repayment from borrowers. The optimal bank capital structure trades off the effects of bank capital on liquidity creation, the expected costs of bank distress, and the ease of forcing borrower repayment. The model can account for phenomena such as the decline in average bank capital in the United States over the last two centuries. It points to overlooked side-effects of policies such as regulatory capital requirements and deposit insurance.

Suggested Citation

  • Douglas W. Diamond & Raghuram G. Rajan, 1999. "A Theory of Bank Capital," NBER Working Papers 7431, National Bureau of Economic Research, Inc.
  • Handle: RePEc:nbr:nberwo:7431
    Note: CF ME

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    JEL classification:

    • G20 - Financial Economics - - Financial Institutions and Services - - - General
    • G21 - Financial Economics - - Financial Institutions and Services - - - Banks; Other Depository Institutions; Micro Finance Institutions; Mortgages

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