The difference between what banks pay on deposits and what they charge on loans is commonly called the net interest margin or lending–deposit spread. That spread reflects a bundle of costs, risks, market structure features, and policy choices. Research by Douglas Diamond of the University of Chicago and Philip Dybvig of Washington University explains how banks’ role in liquidity transformation and deposit protection affects pricing, while Ben Bernanke of the Federal Reserve has shown that monetary policy and funding conditions feed directly into bank margins. Understanding these channels helps explain why spreads vary across banks and countries.
Structural and market factors
Competitive structure, funding mix, and risk pricing are central. Where competition among banks is weak or local branch networks dominate, banks can sustain higher spreads. Raghuram Rajan of the University of Chicago Booth has emphasized how competition interacts with risk-taking incentives, altering pricing behavior. The composition of funding matters: insured retail deposits are cheaper and stickier than wholesale funding, while reliance on volatile market funding raises costs and widens spreads. Credit risk and expected loan losses also push lending rates above deposit rates because banks embed a risk premium and higher provisioning into loan pricing, a point Frederic Mishkin of Columbia University has discussed in his work on financial institutions.
Regulatory and macroeconomic influences
Regulation alters spreads through capital and liquidity requirements, deposit insurance design, and resolution regimes. Stricter capital rules raise banks’ marginal cost of lending, tending to widen spreads, while generous deposit insurance can lower deposit rates. Monetary policy and the shape of the yield curve influence both sides of the margin: a steep yield curve typically supports higher net interest income, while prolonged low rates compress margins. Empirical cross-country work by Stijn Claessens of the World Bank links weaker legal and supervisory frameworks to larger spreads in many emerging markets. These relationships vary with institutional quality and how regulators balance stability and competition.
Consequences reach beyond bank balance sheets. Wider spreads can reduce credit access for households and small firms, slowing investment and widening regional inequalities where banking is thin. Cultural factors that affect trust in banks influence deposit behavior and thus funding costs. Environmental or territorial risks, such as exposure to climate shocks, raise borrower risk and can further increase lending rates in vulnerable regions. Together, these factors explain the persistent yet variable gap between deposit and lending interest rates.