Common Equity Tier 1 (CET1)

Banks can lose money on loans and other assets, so capital funded by owners and accumulated earnings provides a cushion before losses reach some creditors. The Basel framework calls CET1 the highest-quality part of regulatory capital and emphasises common shares and retained earnings as the predominant form of Tier 1 capital.

Qualifying share premium and certain other comprehensive income can also enter, but not every item called equity on an accounting balance sheet qualifies without adjustment. The Basel definition sets eligibility criteria for common shares, including their ability to absorb losses, so a share label alone is insufficient if the instrument's terms do not meet the criteria.

Regulatory adjustments then subtract or change the treatment of specified balance-sheet items, and the Basel CAP30 chapter details these, including goodwill and other intangibles, which are deducted because goodwill may not provide the same readily available loss-absorbing capacity as qualifying common equity when a bank is under stress. CET1 is part of Tier 1 capital, while Additional Tier 1 instruments have different features and form another component, and Tier 2 sits outside Tier 1.

The CET1 ratio uses risk-weighted assets in the denominator, and these weights reflect regulatory approaches to credit, market and operational exposure, not merely the face value of all assets. A bank with $10 billion of CET1 and $100 billion of risk-weighted assets has a 10% ratio, while the same capital over $125 billion of risk-weighted assets yields 8%.

A rise in the ratio can come from retained profits, new qualifying shares or reduced risk-weighted assets, and it does not necessarily mean the bank raised cash by the same amount. Conversely, losses, dividends or a rise in weighted exposures can weaken the ratio, so management needs to watch both numerator and denominator.

A bank can also issue ordinary common shares to improve capital, though existing owners may be diluted, whereas retaining earnings can build CET1 without issuing shares if the earnings qualify. The Basel minimum CET1 ratio is one layer of capital standards, because conservation buffers, countercyclical measures and systemic-bank requirements can raise an institution's effective target under local rules.

Capital requirements vary in implementation, so a reader should check the regulator and reporting date before calling one percentage the bank's current full requirement. CET1 also differs from a liquidity buffer, since a bank may have strong regulatory equity yet face cash-flow stress if funding suddenly leaves.

For depositors, stronger capital may reduce failure risk but does not provide a personal guarantee, because deposit insurance and creditor ranking have separate rules. Investors may compare CET1 ratios across banks, but differences in business mix and risk-weight methods complicate simple rankings.

The useful interpretation is loss-absorbing capacity relative to regulatory risk exposure, read alongside leverage, liquidity, loan quality and supervisory disclosures.