======Interest on Excess Reserves (IOER)======
Interest on Excess Reserves (IOER) is the rate of interest a [[central bank]] pays to [[commercial bank]]s on the funds they hold in their accounts at the central bank above and beyond the legally required minimums. Think of it as a central bank paying interest on a commercial bank's 'checking account' surplus. While the specific term IOER was primarily used by the U.S. [[Federal Reserve]] (the Fed), the concept is a key tool in modern [[monetary policy]] worldwide. Its primary purpose is to help the central bank control short-term interest rates without having to constantly buy or sell government bonds on the open market. By setting a rate at which banks can earn risk-free interest, the central bank establishes a 'floor' for the rate at which banks are willing to lend to each other. This gives policymakers a powerful and precise lever to influence the cost of money throughout the entire economy, steering it towards their goals of stable prices and maximum employment.
===== How IOER Works: The Nitty-Gritty =====
Imagine Bank A has €1 billion in deposits but is only required to keep €100 million as [[reserves]]. The extra €900 million are its 'excess reserves'. Before the widespread use of IOER, Bank A's best option was to lend this excess cash to another bank, say Bank B, in the [[interbank lending market]]. The interest rate on that loan would be determined by the supply and demand for reserves.
Now, let's introduce IOER. The central bank announces it will pay, for example, 3% interest on any excess reserves a bank holds with it. Suddenly, Bank A has a new, completely risk-free option. Why would it lend its €900 million to Bank B for 2.9% if it can get a guaranteed 3% from the central bank? It wouldn't. Therefore, the IOER effectively sets a minimum rate, or a floor, for the interbank lending market. No sane bank will lend to another bank for less than it can earn risk-free from the central bank. This gives the central bank direct influence over the benchmark rates, like the [[federal funds rate]] in the U.S., that underpin all other interest rates in the economy.
===== IOER's Role in Monetary Policy =====
IOER wasn't always a star player in the central banking toolkit. Its prominence grew dramatically in the wake of the [[Global Financial Crisis]] of 2008.
==== Before and After the 2008 Crisis ====
Before 2008, the Fed managed interest rates by making small adjustments to the supply of reserves in the banking system to meet its target rate. However, to combat the crisis, the Fed unleashed several rounds of [[quantitative easing]] (QE), buying trillions of dollars in bonds and flooding the banking system with an ocean of excess reserves. In this new reality, the old method of tweaking a scarce supply of reserves was like trying to manage a flood with a teaspoon. IOER became the primary tool. By raising or lowering the IOER, the Fed could directly steer short-term rates up or down, even with a massive amount of liquidity sloshing around the system.
==== A New Era: From IOER to IORB ====
To simplify things, in July 2021, the Federal Reserve combined the rate on excess reserves (IOER) and the rate on required reserves into a single, unified rate: **[[Interest on Reserve Balances (IORB)]]**. For all practical purposes, IORB functions just like IOER did—it's the main rate the Fed uses to guide the federal funds rate. So, while you might still see the term IOER in older articles, the current and correct term in the U.S. is IORB.
The [[European Central Bank (ECB)]] uses a similar tool, but it's called the [[deposit facility rate]]. It serves the same function: acting as a floor for overnight interbank interest rates in the Eurozone.
===== Why Should a Value Investor Care? =====
Understanding a central bank's plumbing might seem academic, but for a value investor, it's crucial. The rate on reserve balances is a direct signal from the most powerful financial institution on the planet, and it has tangible effects on your portfolio.
  * **Impact on Valuations:** The IORB (or the ECB's deposit facility rate) is a key component of the [[risk-free rate]]. When a value investor calculates the intrinsic value of a company using a [[discounted cash flow (DCF)]] model, the risk-free rate is a fundamental input. A higher IORB leads to a higher risk-free rate, which increases the discount rate applied to a company's future earnings. A higher discount rate means a lower present value for those future earnings, putting downward pressure on stock [[valuation]]s. Simply put: **when risk-free returns go up, the price you're willing to pay for risky assets like stocks should go down**, all else being equal.
  * **Bank Profitability:** For banks, interest on their reserves is a direct, risk-free revenue stream. When the central bank raises the IORB, it's handing banks a risk-free profit boost on the cash they're required to park. When analyzing a bank stock, this can be a significant factor in its net interest margin and overall profitability.
  * **A Barometer for Monetary Policy:** Watching for changes in the IORB is one of the clearest ways to gauge the Fed's intentions. An increase signals a 'hawkish' stance, meaning the Fed is fighting inflation and tightening financial conditions. A decrease signals a 'dovish' stance, indicating a desire to stimulate the economy. For an investor, this provides a vital clue about the direction of the economic winds that will affect every company you own.