Banking & Market Risk7 min read

IRRBB Supervisory Outlier Test: What Banks Must Prove

By Jonas Adam Mohamed Osman, known as Yonas Osman

CEO of Quantica Risk

60 Rue François Ier, 75008 Paris, France

Published 15 October 2026

How the IRRBB supervisory outlier test works, why rising rates exposed banking-book gaps, and what breaching the threshold means in practice.

Executive answer

The interest rate risk in the banking book supervisory outlier test flags institutions whose economic value of equity falls by more than 15% of Tier 1 capital, or whose net interest income would fall materially, under a set of prescribed rate shock scenarios. The 2022-2023 rate cycle turned this from a largely theoretical threshold into a live supervisory concern, as the collapse of several US regional banks demonstrated how quickly unhedged duration mismatches in the banking book can threaten solvency.

Breaching the outlier threshold does not automatically trigger a capital add-on, but it does trigger intensive supervisory dialogue and, typically, a requirement to explain mitigating actions — hedging, balance sheet rebalancing, or capital planning — within a defined timeframe. Banks that model IRRBB only for regulatory reporting, rather than as a live treasury risk management input, consistently find themselves reacting to outlier breaches rather than anticipating them.

Why 2023 was a stress test the industry did not plan

Silicon Valley Bank's failure crystallised a lesson regulators had been signalling for years: available-for-sale and held-to-maturity securities portfolios funded by short-duration deposits create economic value sensitivity that accounting classification can mask from headline capital ratios. European banks, subject to the EBA's binding IRRBB standards since 2023, generally fared better due to tighter standardised outlier thresholds and more active supervisory monitoring, but the episode still prompted a broad reassessment of behavioural assumptions underlying deposit modelling.

The core modelling challenge exposed was deposit behaviour: models calibrated during a decade of near-zero rates assumed deposit stability and limited repricing sensitivity that did not hold once retail and corporate depositors had attractive alternative yields readily available through money market funds and online banks. Recalibrating these behavioural assumptions, rather than simply rerunning existing models with higher rate shocks, has been the more consequential post-2023 workstream for most treasury functions.

Standardised scenarios and the limits of a single test

The outlier test applies six prescribed interest rate shock scenarios — parallel up and down, steepener, flattener, and short rate shocks in both directions — calibrated by currency and updated periodically by the Basel Committee and EBA. While standardisation improves comparability across institutions, it also means the test can miss idiosyncratic risks specific to a bank's actual balance sheet structure, such as concentrated exposure to a particular deposit segment or embedded optionality in mortgage prepayment behaviour.

Supervisors increasingly expect banks to supplement the standardised test with their own internally designed stress scenarios reflecting the bank's specific asset-liability structure, and to demonstrate in ICAAP submissions that Pillar 2 capital adequately covers interest rate risk beyond what the standardised shocks capture. Banks relying solely on the regulatory scenarios for internal risk appetite setting are, in practice, under-managing a risk that the 2023 episode showed can move quickly from a modelling footnote to an existential liquidity event.

Integrating IRRBB with liquidity and capital planning

IRRBB cannot be managed in isolation from liquidity risk, since the same duration mismatches that drive economic value of equity sensitivity also determine how much unrealised loss a bank would crystallise if forced to sell securities to meet deposit outflows — exactly the dynamic that triggered contagion in March 2023. Integrated treasury risk frameworks now explicitly link IRRBB stress outputs to the liquidity coverage ratio's own stress assumptions, rather than running these two programmes with separate governance and separate rate assumptions.

This integration extends to recovery planning: banks are increasingly required to show supervisors how IRRBB-driven losses would interact with recovery indicators and triggers, ensuring that a rate shock severe enough to breach the outlier threshold is also reflected consistently in the bank's broader contingency planning rather than treated as a standalone Pillar 2 metric.

Conclusion

The supervisory outlier test is a floor, not a ceiling, for sound interest rate risk management, and the 2023 banking stress demonstrated clearly that banks treating it as a compliance checkbox rather than a live risk signal can find the gap between regulatory comfort and economic reality closes very fast. Robust deposit behavioural modelling and integration with liquidity stress testing are now the real differentiators between resilient and fragile balance sheets.

Jonas Adam Mohamed Osman, known as Yonas Osman, CEO of Quantica Risk, encourages treasury and ALM teams to validate deposit behavioural assumptions against actual observed repricing every cycle, since outdated assumptions are the single most common source of IRRBB surprises.

Primary sources

IRRBBinterest rate riskbanking bookEBANII sensitivity