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Model #14 • Commercial Banking & Regulatory Desk Live Treasury Curve Hydration Active

Commercial Bank Balance Sheet, Bank Capital & Basel III Underwriter

Q: What is a Bank Duration Gap and why does it matter?

The Duration Gap measures the mismatch in interest rate sensitivity between a bank's assets (loans, bonds) and its liabilities (deposits, debt). Because banks typically borrow short (low duration deposits) and lend long (high duration fixed mortgages and Treasury bonds), their duration gap is positive. When interest rates rise sharply, asset values fall much faster than liabilities decline, directly wiping out bank equity.

Q: What happened to Silicon Valley Bank (SVB) in mathematical terms?

SVB took hundreds of billions in short-term venture deposits and invested them into long-duration Treasury and mortgage bonds (duration ~5.6 years) yielding ~1.6%. When the Fed raised rates by 500 bps, SVB's bond portfolio lost over $21 billion in market value—exceeding the bank's entire Tier 1 equity. When venture clients withdrew uninsured deposits, SVB was forced to sell bonds at a loss, crystalizing the insolvency and triggering an immediate bank run.

Q: What is the difference between AFS (Available-for-Sale) and HTM (Held-to-Maturity)?

AFS securities are marked to market on the balance sheet, with unrealized paper gains/losses recorded in Accumulated Other Comprehensive Income (AOCI). HTM securities are carried at amortized cost, shielding accounting equity from interest rate volatility. However, if a bank is forced to sell even a fraction of HTM assets to meet liquidity needs, it 'taints' the entire portfolio, forcing all HTM bonds to be marked to market.

Q: What are Basel III Capital Conservation Buffers?

Basel III requires banks to hold a minimum CET1 ratio of 4.5% plus an additional 2.5% Capital Conservation Buffer (CCB), bringing the effective threshold to 7.0%. Banks falling into the buffer zone face mandatory restrictions on dividend payouts, share buybacks, and executive bonuses to conserve capital.

Institutional bank asset-liability underwriter. Models duration mismatches, Common Equity Tier 1 (CET1) capital depletion, Supplementary Leverage Ratio (SLR), and Liquidity Coverage Ratio (LCR) under unhedged rate hikes and uninsured deposit flight.

Authoritative Reference METHODOLOGY • COVENANTS • PROOF

Institutional Methodology & Underwriting Dossier

This regulatory underwriter models commercial bank balance sheet vulnerability to interest rate shocks and liquidity runs. It implements Asset-Liability Management (ALM) duration gap equations, Basel III regulatory capital boundaries (CET1, Tier 1, Total Capital, Supplementary Leverage Ratio), Liquidity Coverage Ratio (LCR), and simulates deposit flight scenarios (e.g. Silicon Valley Bank and 2023 regional banking crisis dynamics).

1. Target Audience & Practical Application

How different financial market participants apply this quantitative model to real-world capital allocation:

Commercial Bank Treasurers & ALM Directors

Model balance sheet duration gaps, evaluate interest rate sensitivity on Held-to-Maturity (HTM) vs. Available-for-Sale (AFS) portfolios, and maintain Basel III regulatory compliance.

Bank Equity Research & Hedge Fund Analysts

Stress-test regional banks (KRE) against deposit concentration risks, unrealized security losses, and regulatory capital depletion under aggressive Fed tightening.

Corporate Treasurers & CFOs

Assess bank counterparty solvency before allocating corporate treasury cash balances above the $250,000 FDIC insurance limit.

MBA & Economics Students

Deconstruct the exact mathematical plumbing of the 2023 bank runs—understanding how a positive duration gap transforms rate hikes into immediate equity destruction.

2. Bank ALM Duration Gap & Basel III Capital Formulas

1. Bank Asset-Liability Duration Gap:
Duration Gap = D_A - (L / A) × D_L

2. Bank Equity Sensitivity to Interest Rate Shocks (Δy):
ΔE ≈ -[D_A - (L / A) × D_L] × A × Δy

3. Basel III Common Equity Tier 1 (CET1) Ratio:
CET1 Ratio = Common Equity Tier 1 / Risk-Weighted Assets (RWA) ≥ 4.5% + 2.5% CCB = 7.0%

4. Supplementary Leverage Ratio (SLR):
SLR = Tier 1 Capital / Total Leverage Exposure ≥ 3.0% (5.0% for G-SIBs)

5. Liquidity Coverage Ratio (LCR):
LCR = High-Quality Liquid Assets (HQLA) / Total Net Stressed 30-Day Cash Outflows ≥ 100%

3. Regulatory Frameworks & Solvency Boundaries

HTM Accounting Shield & Hidden Insolvency: Under U.S. GAAP (ASC 320), bonds classified as Held-to-Maturity (HTM) do not reflect market value changes in regulatory capital. When banks face liquidity runs and must sell HTM bonds to raise cash, unrealized losses immediately crystalize, destroying regulatory capital.
Uninsured Deposit Concentration: Deposits above the $250,000 FDIC limit are highly runnable. If uninsured deposits exceed 70% of total funding, a digital run can drain 20% to 40% of liquidity within 24 to 48 hours.
Prompt Corrective Action (PCA) Thresholds: Under FDIC rules, a bank is 'Well Capitalized' if CET1 ≥ 6.5%, 'Adequately Capitalized' if CET1 ≥ 4.5%, 'Undercapitalized' if CET1 < 4.5%, and 'Critically Undercapitalized' if tangible equity < 2.0% of assets (triggering mandatory FDIC receivership).

4. Frequently Asked Questions (FAQ)

What is a Bank Duration Gap and why does it matter?

The Duration Gap measures the mismatch in interest rate sensitivity between a bank's assets (loans, bonds) and its liabilities (deposits, debt). Because banks typically borrow short (low duration deposits) and lend long (high duration fixed mortgages and Treasury bonds), their duration gap is positive. When interest rates rise sharply, asset values fall much faster than liabilities decline, directly wiping out bank equity.

What happened to Silicon Valley Bank (SVB) in mathematical terms?

SVB took hundreds of billions in short-term venture deposits and invested them into long-duration Treasury and mortgage bonds (duration ~5.6 years) yielding ~1.6%. When the Fed raised rates by 500 bps, SVB's bond portfolio lost over $21 billion in market value—exceeding the bank's entire Tier 1 equity. When venture clients withdrew uninsured deposits, SVB was forced to sell bonds at a loss, crystalizing the insolvency and triggering an immediate bank run.

What is the difference between AFS (Available-for-Sale) and HTM (Held-to-Maturity)?

AFS securities are marked to market on the balance sheet, with unrealized paper gains/losses recorded in Accumulated Other Comprehensive Income (AOCI). HTM securities are carried at amortized cost, shielding accounting equity from interest rate volatility. However, if a bank is forced to sell even a fraction of HTM assets to meet liquidity needs, it 'taints' the entire portfolio, forcing all HTM bonds to be marked to market.

What are Basel III Capital Conservation Buffers?

Basel III requires banks to hold a minimum CET1 ratio of 4.5% plus an additional 2.5% Capital Conservation Buffer (CCB), bringing the effective threshold to 7.0%. Banks falling into the buffer zone face mandatory restrictions on dividend payouts, share buybacks, and executive bonuses to conserve capital.

Bank Balance Sheet Profile

Total Assets ($B): $210B

Total Liabilities & Deposits ($B): $192B

Asset Duration $D_A$ (Y):

Liability Duration $D_L$ (Y):

Risk-Weighted Assets (%):

Initial CET1 ($B):

Tier 1 Capital ($B):

HQLA Assets ($B):

Stress Shocks & Run Scenarios

Interest Rate Hike Shock: +200 bps

Uninsured Deposit Flight (% Outflow): 20%

Held-to-Maturity (HTM) Bond Portion (%): 50% HTM losses are masked from accounting capital until deposit runs force bond liquidations.

FDIC Prompt Corrective Action Verdict:

Adequately Capitalized

Net Duration Gap: +5.33 Yrs

CET1 Ratio (Stressed)

8.2%

Reg Min: 4.5% + 2.5% CCB
Base: 12.1%

Supplementary Leverage (SLR)

4.8%

Reg Min: 3.0% (5.0% G-SIB)
Tier 1: $10.2B

Liquidity Coverage (LCR)

112%

Reg Min: ≥ 100%
HQLA Left: $18.5B

Unrealized Bond Loss

-$22.4B

Crystalized: $11.2B
Tangible Eq: -$4.4B

Executive Bank Solvency & Run Telemetry

With an asset duration of 5.6 years funded by short-term liabilities (0.3 years), the bank carries a severe positive duration gap of +5.33 years. A +200 bps rate shock inflicts $22.4B in economic bond losses. When 20% of uninsured deposits flee, the bank must liquidate $38.4B in securities, crystalizing paper losses into real capital depletion and pushing the CET1 ratio below safety limits.