Bank Capital
Bank capital, also called bank equity or regulatory capital, is the difference between a bank's assets and its liabilities, representing the funds contributed by shareholders and retained earnings. Capital acts as a buffer that absorbs losses, protecting depositors and other creditors from loss and reducing the likelihood that a bank will fail. The adequacy and quality of bank capital are central concerns of prudential regulation and of financial stability analysis.
Functions of capital
Bank capital performs several functions. It absorbs unexpected losses, allowing the bank to continue operating and to meet its obligations even when loans or investments lose value. It provides a cushion that protects depositors and the deposit insurance system from loss. It gives shareholders, whose claims are subordinate to those of creditors, an incentive to monitor the bank and to limit risk-taking, since they bear the first losses. It supports confidence, since depositors and creditors are more willing to deal with a well-capitalised bank, reducing the risk of runs.
Because banks operate with high leverage, holding a small amount of capital relative to assets, the capacity to absorb losses is limited. A small decline in asset values can wipe out capital, and if losses exceed capital, the bank becomes insolvent. This fragility is inherent in banking, since the business model involves funding long-term, illiquid assets with short-term, liquid liabilities.
Regulatory capital
Regulatory capital requirements set minimum levels of capital relative to risk-weighted assets. The Basel framework, developed by the Basel Committee on Banking Supervision and implemented in many countries, distinguishes between tiers of capital based on their capacity to absorb losses. Common equity tier one, consisting of common shares and retained earnings, is the highest quality and is subject to the most demanding requirements. Additional tier one and tier two instruments have lower loss-absorbing capacity and are subject to lower minimums.
Following the global financial crisis, the framework was strengthened with higher minimum requirements, a capital conservation buffer, a countercyclical buffer, and a leverage ratio that constrains total leverage independent of risk weights. Requirements for systemically important banks were also raised, reflecting the greater risk they pose to the financial system. The reforms aim to make banks more resilient and to reduce the probability and cost of crises.
Risk-weighted assets and measurement
The denominator of capital ratios, risk-weighted assets, is calculated by assigning risk weights to different categories of assets, reflecting their credit risk. Banks may use standardised approaches prescribed by regulators or internal models approved by supervisors. Internal models, such as the internal ratings-based approach, use the bank's own estimates of default probabilities and loss given default, subject to supervisory approval and constraints.
The use of internal models has been criticised for allowing banks to understate risk and to inflate capital ratios, and for reducing comparability across institutions. Reforms have constrained the use of internal models and introduced floors that limit the reduction in risk weights, aiming to balance risk sensitivity with reliability and comparability.
Capital, risk-taking and crises
The relationship between capital and risk-taking is complex. Higher capital reduces the probability of failure and the social costs of crises, but it also raises the cost of funding for banks, which may pass the cost on to borrowers. The appropriate level of capital involves balancing the benefits of a safer banking system against the costs of more expensive credit and possibly lower growth. Estimates of the optimal level vary, with some studies suggesting that substantially higher capital would bring net social benefits.
Capital regulation is complemented by liquidity requirements, resolution regimes, and macroprudential tools. Resolution frameworks, including bail-in powers, aim to ensure that shareholders and creditors bear losses when a bank fails, rather than taxpayers. Together, these measures form a package designed to make the financial system more resilient while limiting moral hazard and the implicit subsidy from public safety nets.
Capital and bank business models
The appropriate level and composition of capital vary with a bank's business model. Retail banks with diversified loan portfolios and stable deposit funding may operate with lower capital than investment banks engaged in trading and market-making, which face more volatile risk exposures. The Basel framework allows some differentiation across activities, and it imposes additional requirements on globally systemic banks, reflecting the greater risk they pose.
Capital also interacts with the bank's funding structure. Banks financed largely by deposits, which are insured and stable, may need less capital than banks reliant on wholesale funding, which can evaporate quickly under stress. The combination of capital and liquidity requirements shapes the resilience of a bank and its capacity to withstand shocks, and the two are complements rather than substitutes in the regulatory framework.
The cost of bank capital
A central question in the design of capital regulation is the cost of requiring banks to hold more capital. Banks argue that capital is expensive relative to debt, because equity returns must exceed the after-tax cost of debt and because interest payments are tax-deductible while dividends are not. Higher capital requirements, they contend, would raise the cost of credit and reduce lending.
Empirical research on this question has produced a more nuanced picture. Studies using the Modigliani-Miller framework, adjusted for taxes, deposit insurance, and other frictions, often find that the long-run cost of higher capital is modest, because banks can adjust their business models and pass on some costs through lower deposit rates or reduced risk-taking. The estimated costs vary, but many studies conclude that substantially higher capital would bring net social benefits by reducing the frequency and severity of crises.
Resolution and the public safety net
Bank capital is closely linked to resolution frameworks, which determine how failing banks are wound down. Adequate capital, combined with sufficient loss-absorbing capacity, allows a bank to be resolved without recourse to public funds, protecting taxpayers and limiting moral hazard. Bail-in powers require shareholders and creditors to bear losses before public money is used, reinforcing market discipline.
The implicit public guarantee that has historically shielded large banks from the full consequences of failure creates a subsidy that encourages excessive risk-taking and leverage. Capital requirements, liquidity rules, resolution planning, and restrictions on activities together aim to reduce this subsidy and to internalise the costs of failure. The design of these measures, and the balance between financial stability and efficiency, remain at the centre of regulatory policy debates.