Interest Rate Risk in the Banking Book (IRRBB) is the risk that changes in interest rates will adversely affect a bank's earnings or economic value from its non-trading activities. Unlike market risk in the trading book, IRRBB arises from the fundamental business of banking: taking deposits and making loans.
Why IRRBB Matters
Banks inherently engage in maturity transformation — borrowing short-term (deposits) and lending long-term (mortgages, loans). This creates a natural mismatch that exposes them to interest rate movements. A sudden rise in rates can compress margins when deposit rates rise faster than loan yields adjust.
Two Perspectives on IRRBB
Economic Value of Equity (EVE)
EVE measures the change in the present value of all assets minus liabilities when interest rates change. It captures the long-term impact on the bank's net worth.
$$\Delta EVE = \Delta PV(Assets) - \Delta PV(Liabilities)$$
For a bank with longer-duration assets than liabilities, a rate increase would decrease EVE because asset values fall more than liability values.
Net Interest Income (NII)
NII measures the short-term impact on the bank's earnings — the difference between interest income and interest expense. A 1-year or 2-year horizon is typically used.
| Perspective | Time Horizon | Focus | Measure |
|---|---|---|---|
| EVE | Full maturity | Economic value | Present value change |
| NII | 1–2 years | Earnings | Income change |
Key Risk Factors
Gap Risk
The risk arising from timing differences in the repricing of assets and liabilities. A bank with more assets repricing in 5+ years than liabilities faces significant gap risk.
Basis Risk
The risk that different interest rates (e.g., SOFR vs. prime rate) move by different amounts, even when they have the same repricing frequency. Hedging with one rate index while exposed to another creates basis risk.
Option Risk
Many banking book instruments have embedded options that customers can exercise:
- Prepayment risk — Borrowers refinance mortgages when rates fall
- Early withdrawal — Depositors withdraw time deposits when rates rise
- Drawdown risk — Borrowers draw on credit lines when rates change
Yield Curve Risk
Risk arising from changes in the shape of the yield curve — steepening, flattening, or inversion — rather than just parallel shifts.
Regulatory Framework
Basel Committee IRRBB Standards (2016)
The Basel Committee on Banking Supervision issued revised IRRBB standards requiring banks to:
- Measure IRRBB under six prescribed interest rate shock scenarios
- Report results to supervisors under Pillar 2
- Maintain adequate capital for IRRBB (not a Pillar 1 capital charge in most jurisdictions)
- Set internal limits on EVE and NII changes
Six Prescribed Shock Scenarios
| Scenario | Short Rates | Long Rates |
|---|---|---|
| Parallel Up | ↑ | ↑ |
| Parallel Down | ↓ | ↓ |
| Steepener | ↓ | ↑ |
| Flattener | ↑ | ↓ |
| Short Rate Up | ↑ | — |
| Short Rate Down | ↓ | — |
Outlier Test
A bank is considered an "outlier bank" if the decline in EVE under any scenario exceeds 15% of Tier 1 capital. Outlier status triggers enhanced supervisory scrutiny.
Measurement Approaches
Repricing Gap Analysis
The simplest approach: bucket assets and liabilities by repricing maturity and calculate the gap in each time bucket. Multiply gaps by assumed rate changes to estimate NII impact. Simple but ignores basis risk, optionality, and non-parallel yield curve shifts.
Duration/Sensitivity Analysis
Uses duration and convexity to estimate the sensitivity of EVE to rate changes. More sophisticated than gap analysis but still relies on simplifying assumptions.
Simulation Models
Full cash flow simulation models project NII and EVE under various rate scenarios. These models capture:
- Non-linear payoffs from embedded options
- Behavioral assumptions (prepayment speeds, deposit decay)
- Dynamic balance sheet changes
Hedging IRRBB
Common hedging instruments include:
- Interest rate swaps — Transform fixed-rate exposures to floating (or vice versa)
- Caps and floors — Protect against extreme rate movements
- Swaptions — Options on interest rate swaps for uncertain exposures
- Futures and forwards — Short-dated hedging instruments
FRM Exam Relevance
IRRBB is tested in FRM Part 2 under Market Risk and Liquidity Risk. Key exam areas include:
- EVE vs. NII perspectives and when each is appropriate
- Gap analysis methodology and limitations
- Embedded option risk in banking book instruments
- Regulatory shock scenarios and the outlier test
- Duration-based approaches to IRRBB measurement
Master IRRBB concepts to strengthen your understanding of how banks manage their most fundamental risk exposure!