The CET1 ratio, or Common Equity Tier 1 ratio, is a measure of a bank’s core financial strength expressed as a percentage. It compares a bank’s highest-quality capital (common stock, retained earnings, and similar reserves) to its risk-weighted assets. Banks are required to maintain a CET1 ratio of at least 4.5%, though most large banks hold well above that minimum due to additional buffer requirements.
How the CET1 Ratio Is Calculated
The formula is straightforward: divide a bank’s Common Equity Tier 1 capital by its risk-weighted assets, then multiply by 100 to get a percentage.
The numerator, CET1 capital, includes three main components. First, common stock and any related surplus, meaning the money a bank raised by issuing ordinary shares. Second, retained earnings, which are the accumulated profits a bank has kept rather than paid out as dividends. Third, accumulated other comprehensive income, a catch-all for certain unrealized gains and losses on a bank’s balance sheet (such as changes in the value of bond holdings). Together, these represent the purest form of a bank’s own money, the capital that can absorb losses without the bank needing to borrow or restructure debt.
The denominator, risk-weighted assets, is not simply the total value of everything a bank owns. Instead, each asset is weighted based on how risky it is. A U.S. Treasury bond might carry a weight near zero because the risk of default is negligible, while an unsecured consumer loan would carry a much higher weight. This means a bank with a large portfolio of risky loans needs more capital to maintain the same ratio as a bank holding mostly safe assets.
Why the Ratio Matters
CET1 capital is the first line of defense when a bank takes losses. Unlike debt or hybrid instruments that come with repayment obligations, common equity simply absorbs losses. If a bank’s loan portfolio deteriorates, retained earnings shrink and the stock price falls, but the bank doesn’t owe that money to anyone. That’s what makes CET1 the most reliable cushion in a crisis.
For investors and depositors, the CET1 ratio is one of the fastest ways to gauge whether a bank can weather a downturn. A higher ratio means the bank has more of its own capital backing up every dollar of risk it takes on. A low or declining ratio can signal that a bank is either taking on more risk or burning through its reserves.
Minimum Requirements and Capital Buffers
The Basel III framework, which sets global banking standards, requires a minimum CET1 ratio of 4.5%. But that’s only the floor. On top of it, regulators layer several buffers that push the effective requirement significantly higher.
The most universal is the capital conservation buffer of 2.5%. This brings the practical minimum to 7% for most banks. The buffer exists specifically to ensure banks build up capital in good times so they can draw it down during periods of stress without breaching the hard 4.5% minimum.
Banks designated as globally systemically important (often called “too big to fail”) face an additional surcharge. The size of this surcharge varies by institution and is calculated based on factors like a bank’s size, how interconnected it is with other financial institutions, its cross-border activity, and its complexity. The largest banks can face surcharges that push their effective CET1 requirement into the double digits.
Some jurisdictions also impose a countercyclical capital buffer, which regulators can activate during periods of excessive credit growth to cool down lending.
What Happens When Banks Fall Short
Banks that dip below the combined minimum plus buffer don’t immediately face closure, but they do lose the freedom to return money to shareholders. The restrictions follow a sliding scale that gets progressively tighter.
If a bank’s capital conservation buffer exceeds 2.5 percentage points above the minimum, there are no payout restrictions at all. Below that threshold, the limits kick in. A bank with a buffer between 1.875% and 2.5% can distribute no more than 60% of its eligible retained income. Between 1.25% and 1.875%, the cap drops to 40%. Between 0.625% and 1.25%, only 20%. And if the buffer falls to 0.625% or below, the bank cannot pay dividends, buy back shares, or pay discretionary bonuses at all.
These restrictions create a strong incentive for banks to maintain a comfortable margin above the minimum. No CEO wants to announce that regulators have frozen the bank’s dividend. That’s why most major banks target CET1 ratios well above their minimum requirements, typically in the 10% to 13% range.
CET1 vs. Tier 1 Capital
CET1 is the strictest measure of bank capital, but it’s not the only one. Tier 1 capital includes everything in CET1 plus a category called Additional Tier 1 (AT1) capital. AT1 instruments are typically a type of bond that can be converted into equity or written off entirely if the bank’s capital falls below a certain threshold. They’re designed to absorb losses, but they carry contractual obligations that common equity does not.
The minimum Tier 1 ratio (CET1 plus AT1) is 6%, compared to 4.5% for CET1 alone. Beyond Tier 1, banks must also meet a total capital ratio of 8%, which adds in Tier 2 capital like subordinated debt. But CET1 remains the ratio that regulators and analysts watch most closely because it represents the capital with no strings attached.
How to Use CET1 Ratios as an Investor
When comparing banks, look at CET1 ratios in context. A ratio of 11% at one bank and 13% at another doesn’t automatically make the second bank safer. You also need to consider the risk profile of each bank’s assets and how aggressively those assets are weighted. A bank with conservative risk-weighting practices and an 11% ratio may be in a stronger position than one with generous weighting and 13%.
Trends matter more than snapshots. A bank whose CET1 ratio has been declining for several quarters may be growing its loan book faster than its capital base, or it may be absorbing losses. Either way, a sustained downward trend warrants attention. Conversely, a steadily rising ratio suggests the bank is building resilience, though an unusually high ratio might also mean the bank isn’t deploying capital efficiently.
Banks report their CET1 ratios in quarterly earnings releases, usually in the financial highlights or capital adequacy section. Comparing a bank’s reported ratio against its stated target and its regulatory minimum (including all applicable buffers and surcharges) gives you a clear picture of how much headroom it has before restrictions would apply.