Tier 1 Capital Ratio

August 24, 2024 Risk Management

The Tier 1 capital ratio compares a bank's CET1 and eligible Additional Tier 1 capital with its risk-weighted assets.

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The Tier 1 capital ratio compares a bank’s Tier 1 capital with its risk-weighted assets. The numerator consists of Common Equity Tier 1 (CET1) plus eligible Additional Tier 1 (AT1) capital after applicable regulatory adjustments.

It is a risk-based capital ratio. It should not be confused with the Tier 1 leverage ratio, which uses a non-risk-weighted exposure measure.

Key Takeaways

  • Tier 1 capital equals CET1 plus eligible AT1.
  • The denominator is RWA, not total assets.
  • The Basel minimum Tier 1 ratio is 6% before applicable buffers and other requirements.
  • A ratio can rise because Tier 1 capital increases or because RWA decline.
  • A higher ratio usually means more going-concern capital relative to regulatory risk, but it does not prove liquidity, profitability, or safety.

Formula

$$ \text{Tier 1 Capital Ratio} = \frac{\text{Tier 1 Capital}} {\text{Risk-Weighted Assets}} \times 100 $$
$$ \text{Tier 1 Capital} = \text{CET1} + \text{Additional Tier 1} $$

Risk-weighted assets include regulatory amounts for credit, market, and operational risk under the applicable framework.

Worked Example

Assume a bank reports:

ItemAmount
CET1 capital$9.0 billion
Eligible AT1 capital$1.0 billion
Tier 1 capital$10.0 billion
Tier 2 capital$2.0 billion
RWA$100.0 billion
$$ \text{Tier 1 Capital Ratio} = \frac{10}{100} \times 100 = 10.0\% $$

For comparison, the CET1 ratio is 9.0% and the total capital ratio is 12.0%.

If RWA increase to $125 billion while Tier 1 capital remains $10 billion, the Tier 1 ratio falls to 8.0%. The bank did not lose Tier 1 capital, but it has less capital relative to the regulatory risk denominator.

How the Ratio Can Change

DriverTypical effect, all else equal
Retained profitRaises CET1 and Tier 1
Common-share issuanceCan raise CET1 and Tier 1
Eligible AT1 issuanceRaises Tier 1 but not CET1
Dividend, loss, or regulatory deductionCan reduce CET1 and Tier 1
AT1 redemption or loss of eligibilityReduces Tier 1
Growth in higher-risk exposuresCan raise RWA and lower the ratio
Asset sale or risk migrationCan lower RWA and raise the ratio
Rule or model changeCan change RWA without changing accounting assets

A sound ratio bridge separates numerator changes from denominator changes.

Tier 1 Ratio Compared With Other Capital Ratios

RatioNumeratorDenominatorWhat it emphasizes
CET1 ratioCET1RWAHighest-quality common-equity capital
Tier 1 capital ratioCET1 plus eligible AT1RWATotal going-concern capital
Total capital ratioTier 1 plus eligible Tier 2RWAGoing- and gone-concern regulatory capital
Tier 1 leverage ratioTier 1Applicable leverage exposure measureNon-risk-based backstop

A bank can meet the Tier 1 ratio while failing another capital requirement. The ratios are separate constraints, not substitutes.

Basel Minimum and Effective Requirements

The Basel Framework sets a 6% minimum Tier 1 ratio. This headline figure is only a starting point.

The bank may also face:

  • the capital conservation buffer
  • a countercyclical capital buffer
  • systemic-bank surcharges
  • higher national minimums
  • bank-specific supervisory requirements
  • stress-capital or planning constraints
  • management buffers above legal requirements

Because many buffers are CET1-based, a bank cannot necessarily fill all required headroom with AT1.

Why the Tier 1 Ratio Matters

The ratio can influence:

  • distributions and capital conservation
  • AT1 issuance or redemption
  • balance-sheet growth
  • lending and portfolio allocation
  • capital planning and stress testing
  • supervisory intervention
  • funding costs and market confidence

For investors, a useful question is how much durable capital headroom remains after expected losses, distributions, RWA growth, and all applicable requirements.

How to Analyze the Ratio

  1. Confirm the entity and date. Parent, consolidated group, and bank subsidiary ratios may differ.
  2. Reconcile CET1 and AT1. Review earnings, distributions, issuance, redemptions, deductions, and instrument eligibility.
  3. Bridge RWA. Separate credit, market, and operational components and identify model or rule changes.
  4. Measure headroom. Use the full applicable requirement, not only the Basel minimum.
  5. Check quality. Determine how much Tier 1 is CET1 rather than AT1.
  6. Review stress sensitivity. Estimate losses, capital actions, and RWA inflation under adverse assumptions.
  7. Read other measures. Include leverage, liquidity, asset quality, funding, and profitability.

Common Mistakes and Limitations

  • Using total assets as the denominator.
  • Calling Tier 1 capital identical to common equity.
  • Assuming AT1 issuance improves the CET1 ratio.
  • Comparing ratios across jurisdictions without checking rules, scope, and transitions.
  • Treating lower RWA as proof of lower economic risk.
  • Using the 6% Basel minimum as a universal operating target.
  • Assuming a compliant ratio guarantees solvency or access to liquidity.

Authoritative Sources

  • Tier 1 Capital: The ratio’s numerator.
  • Tier 2 Capital: Capital included in total capital but excluded from Tier 1.
  • Risk Weight: An input used in parts of standardized RWA.
  • Basel III: The broader capital, leverage, liquidity, and disclosure framework.

Educational Use

This page provides general financial education, not investment, banking, accounting, legal, or regulatory advice. Use current national rules and official bank disclosures for an actual capital assessment.

Tangible Common Equity
Tier 1 Leverage Ratio
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