5.17: Excess Reserves

Excess reserves, while often viewed as idle funds from a lending perspective, play a vital role in ensuring financial stability and managing risk—particularly during periods of economic uncertainty or regulatory change.

Strategic Value Beyond Liquidity

Excess reserves are not merely a liquidity buffer; they represent a deliberate strategic decision by banks. When economic conditions are stable, lending typically yields higher returns. However, during periods of financial volatility or increased credit risk, banks may prefer to hold their surplus funds with the central bank. This preference reflects the broader principle of liquidity preference, where institutions prioritize secure, immediate access to funds over potential profit.

Regulatory changes also shape this behavior. For example, post-2008 financial reforms introduced under Basel III, such as the Liquidity Coverage Ratio (LCR), require banks to maintain a stock of high-quality liquid assets—reserves included—to meet short-term obligations. As a result, holding excess reserves has become a more permanent and structural feature of modern banking.

Interest on Reserves as a Monetary Policy Tool

The Interest on Reserve Balances (IORB) serves as a key policy instrument in a floor system of monetary policy. By adjusting the IORB rate, the Federal Reserve effectively sets a lower boundary for short-term interest rates. When the IORB is high, banks are incentivized to retain reserves at the Fed, reducing the supply of credit and helping contain inflation. Conversely, a lower IORB makes lending more attractive, encouraging banks to inject liquidity into the economy.

This mechanism gives central banks a precise and flexible way to influence interbank lending rates and overall monetary conditions—particularly in a financial system flush with reserves. Thus, excess reserves have evolved from passive liquidity buffers to active instruments of monetary policy implementation.

Excess reserves are funds that commercial banks hold beyond any mandated minimum. As of late 2025, this requirement is zero in the U.S., so banks hold large reserves for other important reasons.

This is often a precautionary measure. By keeping extra funds highly liquid, banks can prepare for unexpected events, such as large customer withdrawals.

Additionally, during times of economic uncertainty, banks may worry about borrowers defaulting, making it feel safer to hold onto reserves.

In the U.S., these excess reserves are typically deposited with the Federal Reserve, where banks earn interest on them through Interest on Reserve Balances (IORB). The Fed uses the IORB rate as a key tool to influence economic conditions.

By increasing the IORB rate, the Fed encourages banks to hold their reserves instead of lending, which helps slow economic activity.

On the other hand, lowering the IORB rate makes it less attractive for banks to keep excess reserves, creating an incentive for them to lend more and help stimulate the economy.