AI for Bank Regulatory Capital: Claude Tools for Basel III, CET1, and RWA Calculations

Bank Regulatory Capital and AI

Banking regulation requires financial institutions to maintain sufficient capital buffers against unexpected losses. The Basel III framework — implemented through CRR/CRD in Europe and US prudential rules — sets minimum capital requirements expressed as ratios of regulatory capital to risk-weighted assets (RWA). Compliance failures can trigger supervisory action, dividend restrictions, or resolution. Claude with ClaudeFinLab models CET1 ratios, RWA compositions, leverage ratios, stress tests, and capital planning frameworks used by bank treasury and risk teams.

CET1 and Capital Ratio Calculations

• "Basel III capital ratios for a US regional bank: Total assets $85B. Regulatory capital stack: Common Equity Tier 1 (CET1) = paid-in capital + retained earnings − goodwill/intangibles − deferred tax assets above threshold = $4.2B + $3.8B − $0.9B − $0.4B = $6.7B. Additional Tier 1 (AT1) = qualifying perpetual preferred + AT1 instruments = $0.8B. Tier 1 capital = CET1 + AT1 = $7.5B. Tier 2 capital = qualifying subordinated debt + general provisions = $1.2B. Total regulatory capital = $8.7B. Risk-weighted assets: $52B. CET1 ratio = $6.7B / $52B = 12.88%. Tier 1 ratio = $7.5B / $52B = 14.42%. Total Capital ratio = $8.7B / $52B = 16.73%. Basel III minimums: CET1 4.5% + capital conservation buffer 2.5% = 7.0% minimum; this bank is well-capitalized."
• "Capital conservation buffer mechanics: bank with CET1 ratio 8.5% (above 7.0% threshold but below 8.0% upper buffer). Distribution restrictions apply: maximum distributable amount (MDA) = 60% of profits (25-75% restriction schedule based on buffer distance). If CET1 falls to 7.5%: restricted to paying 20% of earnings as dividends. Implication for capital planning: maintain CET1 ≥ 9.5% to keep MDA at 100% (no payout restrictions) during stress periods."

Risk-Weighted Asset (RWA) Calculation

• "Credit RWA under standardized approach: loan portfolio of $30B. Residential mortgages (LTV <80%): $12B × 50% risk weight = $6.0B RWA. Commercial real estate: $8B × 100% RW = $8.0B RWA. Corporate loans (A-rated): $5B × 100% RW = $5.0B RWA. Sovereign exposures (US Treasuries): $3B × 0% RW = $0 RWA. Retail exposures: $2B × 75% RW = $1.5B RWA. Total credit RWA = $20.5B. Market RWA (standardized): $4B trading book × VaR multiplier = $1.8B. Operational RWA (basic indicator): gross income $2.5B × 15% = $375M. Total RWA = $20.5B + $1.8B + $0.375B = $22.675B."
• "Internal ratings-based (IRB) approach comparison: same $5B corporate loan book. Standardized → 100% RW → $5.0B RWA. Under IRB: PD (probability of default) 0.40% (internal model), LGD (loss given default) 45% (unsecured), EAD $5B, maturity 3 years. IRB formula produces risk weight ~55% for this PD/LGD combination → $5B × 55% = $2.75B RWA. IRB benefit: saves $2.25B of RWA → at 10% CET1 ratio, frees $225M of capital → improves ROE. Requires regulatory model approval — typically 3-5 year development and validation process."

Leverage Ratio

• "Leverage ratio calculation: bank with $85B total assets, $7.5B Tier 1 capital. Leverage exposure (denominator): on-balance-sheet assets $85B + off-balance-sheet exposures (derivatives, commitments, SFTs): derivatives (net replacement cost + add-on) $3.2B; undrawn credit commitments × 10% CCF $1.8B; securities financing transactions $2.5B. Total leverage exposure = $85B + $3.2B + $1.8B + $2.5B = $92.5B. Leverage ratio = $7.5B / $92.5B = 8.11%. US enhanced supplementary leverage ratio (eSLR) minimum for G-SIBs: 5% (holding company) / 6% (bank subsidiary). This regional bank comfortably exceeds the 4% Basel minimum."

DFAST / Capital Stress Testing

• "DFAST severely adverse scenario impact: starting CET1 10.5%. Stress scenario (9-quarter horizon): GDP decline −5.0%, unemployment peak 12%, house price decline −25%, equity market decline −50%, credit losses elevated. Projected loan losses over 9 quarters: $2.8B (3.3% of loans). Pre-provision net revenue: $1.9B. Net stress income: −$0.9B. AOCI impact: −$0.4B (rate-related AFS losses). DTA limitation adjustment: −$0.1B. RWA increase under stress: +$3B (downgrades increase risk weights). Stressed CET1 = ($6.7B − $0.9B − $0.4B − $0.1B) / ($52B + $3B) = $5.3B / $55B = 9.6%. Above 4.5% minimum — passes stress test. Conclusion: bank has $2.8B of capital headroom above CET1 floor."

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