How does the FRTB define the boundary between the trading book and banking book, and why was it redesigned?

The trading book/banking book boundary is one of the most fundamental concepts in bank capital regulation, and the FRTB redesigned it to close a major regulatory arbitrage that existed under Basel II/II.5.

The Old Problem

Under the pre-FRTB framework, the boundary was largely based on trading intent. Banks would classify positions as trading book or banking book depending on which produced lower capital requirements. This led to:

• Regulatory arbitrage: Complex credit instruments (CDOs, CLOs) were placed in the trading book when market risk capital was lower, or moved to the banking book when credit risk capital was lower
• Boundary hopping: Banks switched positions between books when capital rules changed
• Inconsistent treatment: Similar positions at different banks could be in different books

The FRTB Solution: Presumptive List + Strict Controls

The FRTB introduces:

1. Presumptive Assignment

Certain instruments are presumptively in the trading book:

• Instruments held for short-term resale
• Instruments held for market-making
• Positions hedging other trading book instruments
• Listed equities, trading-related repo/reverse repo

Certain instruments are presumptively in the banking book:

• Unlisted equities
• Instruments designated for securitization warehousing
• Real estate holdings
• Retail and wholesale lending

2. Internal Transfers

If a bank internally hedges a banking book exposure using a trading book instrument, strict rules apply:

• The hedge must be with an external third party (or an internal risk management desk that immediately hedges externally)
• The banking book position retains its original capital treatment
• Capital relief only applies to the extent of the external hedge

3. Switching Restrictions

Moving positions between books is heavily restricted:

• Requires senior management and regulatory approval
• A capital benefit test is applied — if switching reduces capital, the bank must hold the HIGHER of the two calculations
• Re-designation is considered irrevocable in most cases

Impact on Banks

• Larger trading books — some instruments that were previously in the banking book may be forced into the trading book
• Higher capital — the capital benefit test prevents arbitrage gains from switching
• Operational burden — banks need robust systems to track and enforce the boundary
• CVA capital — the boundary also affects whether CVA risk charges apply

FRM exam tip: Know the presumptive assignment rules and understand why the boundary matters — it determines which capital framework (market risk vs. credit risk) applies to each position.

For more on FRTB boundary rules, check our FRM Part II course.