CET1 Ratio
Executive Summary
Key Takeaways
- ✓ The CET1 ratio expresses Common Equity Tier 1 capital as a percentage of risk-weighted assets, the most closely watched capital adequacy metric under Basel III.
- ✓ The ratio is subject to both a hard minimum requirement and additional capital buffers, and breaching a buffer carries different consequences than breaching the hard minimum, a distinction the model should preserve.
- ✓ Because risk-weighted assets form the denominator, the CET1 ratio is sensitive to both the capital numerator and the risk-weighting methodology applied to the balance sheet — a change in either moves the ratio.
- ✓ The CET1 ratio should be calculated as a live output of the model's own capital and risk-weighted asset build, not a separately maintained reporting figure reconciled only periodically.
- ✓ A rising CET1 ratio achieved purely through balance sheet shrinkage (reducing risk-weighted assets rather than growing capital) represents a different underlying story than one achieved through retained earnings growth, and a model should make that distinction visible.
Definition¶
The CET1 ratio expresses Common Equity Tier 1 capital — a bank's highest-quality, most loss-absorbing capital — as a percentage of risk-weighted assets. It is the most closely watched capital adequacy metric under the Basel III framework.
Calculation¶
CET1 Ratio = CET1 Capital ÷ Risk-Weighted Assets
Minimum Requirements and Buffers¶
The CET1 ratio is subject to both a hard minimum requirement and additional capital buffers layered on top — see Basel Capital Ratios. Breaching a buffer while remaining above the hard minimum typically restricts discretionary distributions rather than constituting the more severe consequence of breaching the minimum itself, a distinction a model should preserve by tracking each threshold separately.
Two Drivers, Not One¶
The CET1 ratio moves with changes in either its numerator (CET1 capital) or its denominator (risk-weighted assets). A rising ratio achieved through balance sheet shrinkage or a shift toward lower-risk-weight assets tells a different story than one achieved through genuine capital growth via retained earnings — a model should present both drivers so a reader can distinguish the two, rather than reporting the ratio's movement without explanation.
Audit Considerations¶
- Confirm the CET1 ratio is calculated as a live output of the model's own CET1 capital and risk-weighted asset build, not a separately maintained figure.
- Confirm minimum requirements and buffers are tracked as distinct, separately labelled thresholds.
- Confirm any ratio movement is explained with reference to both the capital and risk-weighted asset drivers, not presented as a single unexplained change.
Common Errors¶
| Error | Description | Risk |
|---|---|---|
| Disconnected calculation | CET1 ratio maintained separately from the model's own capital and RWA build | Ratio drifts out of consistency with the rest of the forecast |
| Blended threshold | Minimum requirement and buffers collapsed into one figure | Reader cannot tell which type of constraint a scenario would trigger |
| Unexplained movement | Ratio change reported without identifying whether capital or RWA drove it | Balance-sheet-shrinkage-driven improvement misread as capital strength |
Continue Reading¶
Prerequisites¶
- CET1 Modelling — the parent guide
- Basel Capital Ratios
Related Technical Guides¶
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Frequently Asked Questions
What is the CET1 ratio?
Common Equity Tier 1 capital expressed as a percentage of risk-weighted assets, the most closely watched capital adequacy metric under the Basel III framework.
How is the CET1 ratio calculated?
CET1 Ratio = CET1 Capital ÷ Risk-Weighted Assets — see CET1 Modelling for how the numerator is built and Risk Weighted Assets for how the denominator is built.
What is the difference between the minimum requirement and the buffers layered on top?
The minimum is a hard regulatory floor; buffers (the capital conservation buffer, a countercyclical buffer, and a systemic-importance buffer for certain institutions) sit above it, and breaching a buffer typically restricts discretionary distributions rather than constituting an immediate breach of the hard minimum — see Basel Capital Ratios.
Can the CET1 ratio improve without the bank raising more capital?
Yes — reducing risk-weighted assets (through balance sheet shrinkage, a shift to lower-risk-weight assets, or improved risk-weighting methodology) also raises the ratio, which is why the ratio's movement should always be explained by both its numerator and denominator drivers, not assumed to reflect capital growth alone.
Should the CET1 ratio be calculated separately from the model's own forecast?
No — it should be a live output of the model's own CET1 capital roll-forward and risk-weighted asset build, so any forecast scenario immediately shows its effect on the ratio, rather than requiring a separate reconciliation exercise.
Why is the CET1 ratio the most closely watched Basel ratio?
Because CET1 is the highest-quality, most loss-absorbing layer of regulatory capital, making its ratio to risk-weighted assets the clearest single indicator of a bank's capacity to absorb losses before regulatory intervention would be required.
Related Articles
CET1 Modelling
Common Equity Tier 1 (CET1) capital is the highest-quality, most loss-absorbing layer of regulatory capital, and it is the numerator of the most closely watched Basel ratio. This guide covers how to build the CET1 capital base in a model: the eligible components (common shares, retained earnings, certain reserves), the regulatory deductions applied (goodwill, certain deferred tax assets, other intangibles), and how the balance should roll forward period over period as retained earnings and other capital actions occur.
Basel Capital Ratios
The Basel III framework defines three core capital ratios — Common Equity Tier 1, Tier 1, and total capital — each measured against risk-weighted assets, layered with additional capital buffers above the hard minimums. This guide sets out the ratio definitions, the minimum and buffer levels the framework establishes, and how a bank model should represent each ratio and buffer as a distinct, named threshold rather than a single blended capital requirement.
Risk Weighted Assets
Risk-weighted assets (RWA) convert a bank's balance sheet exposures into a common risk-adjusted base, applying higher weights to riskier exposures and lower weights to safer ones. RWA forms the denominator of every Basel capital ratio, making the risk-weighting methodology a first-order driver of reported capital strength. This guide covers the standardized and internal ratings-based (IRB) approaches to calculating RWA, how a model should build the RWA base from segmented exposures, and how risk-weight density should be tracked as its own diagnostic output.
Capital Adequacy Models
Capital adequacy modelling represents the constraint regulatory capital requirements place on how much risk-weighted balance sheet a bank can carry against its available capital base. This guide covers how to structure a capital adequacy model — the capital tiers, the risk-weighted asset base they are measured against, minimum ratio and buffer requirements — and how it should be built as a live check against the balance sheet forecast rather than a standalone reporting exercise calculated after the forecast is already complete.