SUNANDO ROY – On Banking, Finance and Society

In an era of heightened interest rate volatility, banking supervisors have sharpened their focus on Interest Rate Risk in the Banking Book (IRRBB). A cornerstone of this regulatory push is the Supervisory Outlier Test (SOT)—a standardized stress test that evaluates a bank’s vulnerability to interest rate shifts, particularly as they affect its Economic Value of Equity (EVE) and Net Interest Income (NII). Within the European Union (EU), this test has been codified through detailed Regulatory Technical Standards (RTS) issued by the European Banking Authority (EBA). This blog explores the process and complexities of the SOT as implemented in the EU, compares it with the global Basel framework, and outlines the practical implications for banks.

The SOT was formalized in the EU through amendments to Article 98(5a) of Directive 2013/36/EU, tasking competent authorities with identifying banks whose IRRBB exposure, under supervisory stress scenarios, results in significant declines in EVE or NII. Specifically, the RTS define a supervisory outlier as a bank experiencing either a drop in EVE exceeding 15% of Tier 1 capital or a “large decline” in NII, which has been calibrated as a drop of more than 2.5% of Tier 1 capital (European Banking Authority 2022).

The Mechanics of the SOT: EVE and NII

The SOT on EVE requires banks to simulate the long-term impact of interest rate shocks on the present value of all cash flows from interest-sensitive assets and liabilities. The RTS prescribe six interest rate shock scenarios: parallel up, parallel down, steepener, flattener, short rates up, and short rates down. Banks must use a run-off balance sheet assumption—positions are allowed to amortize without being replaced. The results are then aggregated across currencies, with a nuanced approach that partially includes positive valuation changes, unlike the more conservative Basel approach which disregards gains (European Banking Authority 2022).

On the other hand, the SOT on NII is designed to assess the short-term earnings impact. Only two scenarios—parallel up and down shocks—are applied. Here, banks must assume a constant balance sheet over a one-year horizon, where maturing assets and liabilities are replaced with new ones that have comparable risk profiles. Importantly, commercial margins and spread components must be included in the NII calculation, aligning with how banks actually manage IRRBB (European Banking Authority 2022). The EBA’s decision to set a quantitative threshold for NII SOT—absent in Basel’s framework—introduces clarity but also complexity.

Key Implementation Challenges

Implementing the SOTs comes with numerous operational and methodological complexities. One major challenge is data granularity. Banks must model detailed cash flow structures across all relevant currencies and maturity buckets. The inclusion or exclusion of commercial margins introduces further complexity: they are mandatory for NII, but optional for EVE, provided the bank follows a consistent and transparent methodology.

Modeling assumptions diverge between EVE and NII, demanding banks operate with dual approaches—run-off vs. constant balance sheets—which increases operational burdens. Moreover, shock calibration is tailored by currency based on long-term historical interest rate data. This leads to asymmetries in stress intensity, especially for banks operating in multiple jurisdictions (European Banking Authority 2022).

Comparing EU and Basel Approaches

The EU’s implementation of the SOTs is largely inspired by the Basel Committee on Banking Supervision (BCBS) framework. The Basel standards also stipulate a 15% threshold for EVE decline but leave the implementation of an NII-based SOT to national discretion (Bank for International Settlements 2016). The EU has gone further by setting a specific threshold for NII and detailing shock scenarios and modeling assumptions. Additionally, Basel’s more conservative stance does not permit any offset from gains across currencies, whereas the EU applies weighting factors that allow partial recognition.

The treatment of balance sheets also differs. Basel allows more flexibility, while the EU mandates a constant balance sheet for NII and a run-off approach for EVE, increasing comparability but reducing adaptability to banks’ real strategies. Moreover, the EU has recalibrated the interest rate floor for post-shock scenarios, lowering it to -150 basis points from the earlier -100, with a slope of 3 bps/year to reflect recent yield curve behaviors (European Banking Authority 2022).

Supervisory Purpose and Future Outlook

These SOTs are not just compliance tools—they play a critical role in the Supervisory Review and Evaluation Process (SREP). If a bank breaches either threshold, regulators are empowered to demand additional capital, restrict risk-taking activities, or revise internal models. However, supervisors retain discretion and may waive enforcement if IRRBB is judged to be well-managed.

Looking forward, the complexity and cost of SOT compliance will likely incentivize banks to upgrade their IRRBB frameworks, ensuring more dynamic, integrated, and automated risk measurement systems. As interest rate environments become more volatile, the SOTs will remain an essential benchmark of resilience and governance in the banking sector.

Annexure I: Glossary

• IRRBB (Interest Rate Risk in the Banking Book): Risk to a bank’s capital or earnings arising from adverse movements in interest rates affecting banking book positions.
• SOT (Supervisory Outlier Test): A regulatory test evaluating whether changes in interest rates would significantly impact a bank’s EVE or NII.
• EVE (Economic Value of Equity): The net present value of all future cash flows from a bank’s assets and liabilities; a measure of long-term interest rate risk.
• NII (Net Interest Income): The difference between interest income and interest expenses; a short-term measure of profitability under IRRBB.
• RTS (Regulatory Technical Standards): Binding EU legal standards specifying how financial institutions must implement specific regulatory requirements.
• Tier 1 Capital: Core capital that includes equity capital and disclosed reserves; a key indicator of a bank’s financial strength.
• Run-Off Balance Sheet: Assumes existing positions mature over time and are not replaced.
• Constant Balance Sheet: Assumes maturing positions are replaced with similar instruments, maintaining size and structure.
• Shock Scenarios: Hypothetical interest rate changes (parallel, steepener, flattener, etc.) used to stress test IRRBB.
• SREP (Supervisory Review and Evaluation Process): The process by which supervisors assess a bank’s risk profile and capital adequacy.

References

• Bank for International Settlements. Interest Rate Risk in the Banking Book. Basel Committee on Banking Supervision. April 2016.
• European Banking Authority. Final Draft Regulatory Technical Standards on the IRRBB Supervisory Outlier Test under Article 98(5a) of Directive 2013/36/EU. October 20, 2022.
• European Banking Authority. “EBA Publishes Final Standards and Guidelines on Interest Rate Risk and Credit Spread Risk Arising from Non-Trading Book Activities.” October 31, 2022.
• KPMG. “The New EBA Package on IRRBB and CSRBB.” December 2021.
• Risk.net. “Shocks to the System: How Basel IRRBB Update Affects New EU Test.” March 2023.