IOER (Interest on Excess Reserves, deprecated)

What Was IOER?

IOER (Interest on Excess Reserves) was the Federal Reserve's term, used from October 2008 through July 2021, for the rate paid on the excess reserves that commercial banks held at the Fed. "Excess" reserves were the amount banks held above the legally required reserve ratio. The Fed adopted the IORB (Interest on Reserve Balances) terminology in July 2021 after eliminating the legal distinction between required and excess reserves.

IOER and IORB are functionally identical. IOER is now the deprecated term; modern documentation, FOMC statements, and academic references use IORB. References to IOER in pre-2021 literature should be treated as direct precursors to IORB.

Why the Terminology Changed

The Fed eliminated reserve requirements in March 2020 as part of pandemic-era policy normalization. Reserve requirements had become operationally meaningless: with abundant reserves from QE and active liquidity management via the administered-rate framework, the requirement no longer constrained bank behaviour. Eliminating it simplified the framework.

With no required reserves, the distinction between "required" and "excess" reserves became vacuous. All reserves became simply "reserve balances", and the rate paid on them became IORB rather than IOER. The 2021 terminology update reflected the underlying conceptual change.

How to Read Older Sources

When reading academic papers, FOMC minutes, or analyst notes from 2008-2020, treat IOER as the operational equivalent of IORB. The rate setting, policy purpose, and market mechanism are unchanged. The September 2019 repo crisis was triggered partly by inadequate IOER setting; the same dynamics would today involve IORB.

The transition is purely cosmetic. There is no need to re-interpret pre-2021 monetary policy literature in light of the terminology change; the underlying mechanisms are identical.

Historical Context

IOER was introduced in October 2008 as part of the Fed's emergency response to the financial crisis. The Emergency Economic Stabilization Act of 2008 granted the Fed authority to pay interest on reserves, accelerating implementation that had been planned for 2011.

The rate was set at 0.25% from 2008-2015 (during ZIRP), then adjusted incrementally during 2015-2019. The September 2019 repo crisis prompted technical adjustments to keep EFFR within the target range. The transition to IORB in July 2021 was the final step in the post-2008 framework normalization.

For all practical trading and research purposes, treat IOER and IORB as the same concept. Use the current IORB terminology in any new analysis.