Common Equity Tier 1 (CET1)

What Is Common Equity Tier 1 (CET1)?

Common Equity Tier 1, or CET1, is the highest-quality form of regulatory capital under modern bank capital rules. It generally consists of common shares, retained earnings, certain accumulated other comprehensive income, qualifying minority interests, and required regulatory adjustments.

CET1 matters because it is the first layer of capital available to absorb losses while a bank continues operating. Regulators, investors, depositors, and counterparties watch CET1 because thin capital can turn loan losses, market losses, or funding stress into a solvency problem.

Basic Formula

The main ratio is:

In this expression, CET1 capital is the numerator and risk-weighted assets are the denominator. Risk-weighted assets adjust assets and exposures for regulatory risk weights, so a dollar of a low-risk exposure may not receive the same denominator treatment as a dollar of a higher-risk loan.

For example, if a bank has $45 billion of CET1 capital and $500 billion of risk-weighted assets, its CET1 ratio is 9 percent.

What Counts in CET1

CET1 is designed to emphasize capital that can absorb losses without forcing the bank to stop operating. Common equity and retained earnings are central because they sit behind creditors and depositors in the claim hierarchy.

Regulatory adjustments are important. Items such as goodwill, certain deferred tax assets, intangible assets, and other exposures may be deducted or adjusted because regulators do not treat all accounting equity as equally loss-absorbing in stress.

Why Regulators Care

Banking is built on leverage. Banks borrow through deposits and other funding sources, then hold loans, securities, and other assets. Capital is the cushion between asset losses and claims from depositors, lenders, and other creditors.

CET1 requirements are intended to make banks more resilient. A bank with stronger CET1 can absorb more losses before its viability is threatened. That resilience can reduce the likelihood that ordinary credit losses become a systemic problem.

Investor Reading

Investors compare CET1 ratios across banks, but the comparison is not mechanical. A bank with a higher CET1 ratio may still carry higher risk if its assets are weaker, its earnings are volatile, or its funding is fragile. A bank with a lower ratio may be acceptable if its business is stable and it has strong profitability and liquidity.

Trends matter. A falling CET1 ratio can reflect loan growth, buybacks, dividends, losses, acquisitions, or changes in risk-weighted assets. A rising ratio can reflect retained earnings, capital issuance, asset shrinkage, or lower risk weights.

CET1 Versus Tier 1 Capital

CET1 is part of Tier 1 capital, but it is not the whole category. Tier 1 capital can also include Additional Tier 1 instruments that meet regulatory criteria. CET1 is the common-equity core, while AT1 instruments have different terms and loss-absorption features.

That distinction matters because CET1 is generally viewed as the purest capital measure. When stress rises, investors often focus on CET1 before broader capital ratios.

Capital buffers above the minimum are also important. A bank can meet the stated minimum and still face restrictions, market pressure, or supervisory concern if stress losses would push it too close to the line. That is why large-bank disclosures often discuss required buffers, stress-test results, and management's target capital range.

CET1 is not the same as cash. It is a regulatory capital measure based on accounting equity and supervisory adjustments. A bank also needs liquidity to meet withdrawals and funding demands, so capital strength and liquidity strength should be evaluated together.

The Bottom Line

Common Equity Tier 1 is a bank's core loss-absorbing regulatory capital. The CET1 ratio is one of the most important bank safety measures, but it should be interpreted with asset quality, earnings power, liquidity, and the bank's broader risk profile.