Bank CET1 Capital Ratio: How Bank Capital Works

Key Takeaways

• The CET1 capital ratio divides the highest-quality bank capital by risk-weighted assets; Basel III sets a 4.5 percent minimum, but large US banks target 11 to 13 percent in practice.
• G-SIBs face CET1 requirements of 9.5 percent or more before the Federal Reserve's stressed capital buffer is added, so reported ratios near the minimum are a warning, not a comfort.
• A common mistake is comparing CET1 to equity divided by total assets; RWA is much smaller than total assets, so two banks with the same book equity can have very different CET1 ratios.
• Falling below the combined buffer requirement triggers automatic restrictions on dividends, buybacks, and AT1 coupons under the Maximum Distributable Amount framework.

What It Is

A bank's regulatory capital is the cushion that absorbs losses before depositors or taxpayers are exposed. Basel III, the international framework written in response to the 2008 financial crisis, defines three tiers of capital and measures each one against risk-weighted assets (RWA) rather than total assets.

The headline metric is the Common Equity Tier 1 ratio (CET1 ratio). CET1 is the highest-quality capital: common shares, retained earnings, accumulated other comprehensive income, minority interest that qualifies, and a narrow list of regulatory adjustments. Dividing CET1 by RWA gives the CET1 ratio, which Basel III sets at a 4.5 percent minimum, plus a 2.5 percent capital conservation buffer, plus a surcharge of up to 3.5 percent for global systemically important banks (G-SIBs) such as JPMorgan, HSBC, or Citigroup.

The Intuition

Assets are not all equally risky. A US Treasury bill is far less likely to lose value than a commercial real estate loan or a leveraged buyout loan. Basel III therefore requires banks to hold more capital against riskier exposures. That is why the denominator is risk-weighted assets rather than plain total assets. A dollar of cash might carry a 0 percent risk weight. A typical corporate loan carries 100 percent. A high-yield bond can carry much more. RWA is the sum of each exposure times its applicable weight.

The CET1 ratio is the lens regulators look through to decide whether a bank can pay dividends, buy back stock, acquire another bank, or needs to slow down. It is also the metric that determines whether a bank is solvent in a stress test.

How It Works

There are three main capital ratios in the Basel III framework, plus a non-risk-based leverage ratio:

CET1 Ratio        = CET1 Capital / Risk-Weighted Assets
Tier 1 Ratio      = (CET1 + Additional Tier 1) / Risk-Weighted Assets
Total Capital Ratio = (Tier 1 + Tier 2) / Risk-Weighted Assets
Leverage Ratio    = Tier 1 Capital / Total Exposure (on + off balance sheet)

Basel III minimums for every bank:

• CET1 ratio: 4.5 percent
• Tier 1 ratio: 6.0 percent
• Total capital ratio: 8.0 percent
• Leverage ratio: 3.0 percent (higher for US G-SIBs, typically 5 percent at the bank holding company and 6 percent at insured subsidiaries)

On top of the minimums, every bank must hold:

• A capital conservation buffer of 2.5 percent CET1
• A countercyclical buffer of 0 to 2.5 percent CET1, turned on by national regulators during credit booms
• A G-SIB surcharge of 1 to 3.5 percent CET1, scaled to size, interconnectedness, complexity, cross-jurisdictional activity, and substitutability

A US G-SIB with a 2.5 percent surcharge therefore needs CET1 of at least 9.5 percent (4.5 + 2.5 + 2.5) before any US-specific stressed capital buffer (SCB) from the Federal Reserve's annual stress test is added. Large US banks typically target CET1 ratios of 11 to 13 percent to maintain a management buffer above the all-in requirement.

Additional Tier 1 (AT1) includes perpetual preferred stock and contingent convertible bonds that absorb losses on a going-concern basis. Tier 2 includes subordinated debt and qualifying loan loss reserves that absorb losses in a gone-concern (liquidation) scenario.

Falling below the combined buffer requirement triggers an automatic restriction on dividends, bonuses, and AT1 coupons under the Maximum Distributable Amount (MDA) framework.

Worked Example

Consider a large US bank reporting at year end:

• Common equity Tier 1 capital: 240,000 million
• Additional Tier 1 capital: 25,000 million
• Tier 2 capital: 35,000 million
• Risk-weighted assets: 2,000,000 million
• Total leverage exposure: 3,400,000 million

Ratios:

CET1 Ratio        = 240,000 / 2,000,000 = 12.0%
Tier 1 Ratio      = (240,000 + 25,000) / 2,000,000 = 13.25%
Total Capital Ratio = (240,000 + 25,000 + 35,000) / 2,000,000 = 15.0%
Leverage Ratio    = 265,000 / 3,400,000 = 7.8%

If this bank is designated a G-SIB with a 2.5 percent surcharge and a Fed SCB of 3.0 percent, the all-in CET1 minimum is 4.5 + 2.5 + 2.5 + 3.0 = 12.5 percent. At 12.0 percent, the bank is below its SCB floor, and the MDA framework would restrict capital distributions until the ratio is rebuilt.

Common Mistakes

1. Comparing CET1 to equity divided by total assets. CET1 uses RWA in the denominator, not total assets. A bank with 8 percent equity to total assets could easily have a 15 percent CET1 ratio because its RWA is far smaller than its balance sheet. Mixing the two is one of the most common errors in bank analysis.

2. Ignoring the leverage ratio. A bank can game RWA-based ratios by piling into low-risk-weight assets like Treasuries and agency mortgage-backed securities. The Basel leverage ratio and the US Supplementary Leverage Ratio exist precisely to cap that behavior. Always check both.

3. Treating the minimum as the target. No well-run bank manages to the 4.5 percent CET1 minimum. Between conservation buffers, G-SIB surcharges, SCBs, and a management buffer, the operating target at a large US bank is usually 11 to 13 percent. Missing that framing makes reported ratios look misleadingly abundant.

4. Confusing book equity with CET1. Goodwill, most deferred tax assets, mortgage servicing rights above threshold, and investments in unconsolidated financial institutions are deducted from CET1. Two banks with the same book equity can have very different CET1 depending on intangibles and DTA balances.

5. Forgetting AOCI. Under current US rules for Category I and II banks, unrealized losses on available-for-sale securities flow through CET1. The 2023 regional bank stress episode exposed firms that believed held-to-maturity losses were invisible to regulatory capital. For the largest banks, that belief was wrong, and changes under Basel III Endgame will tighten the treatment further for additional firms.

Frequently Asked Questions

Q: What is the CET1 capital ratio in simple terms? The CET1 ratio is the percentage of a bank's risk-weighted assets funded by its highest-quality capital, common shares and retained earnings. A higher ratio means the bank has more of its own money absorbing losses before depositors or taxpayers are exposed.

Q: How does the CET1 capital ratio affect investment decisions? CET1 is the gatekeeper for dividends and buybacks. A bank below its all-in CET1 requirement cannot distribute capital freely. Investors watch whether a bank's ratio sits comfortably above its requirement, because the buffer above the floor is available for shareholder returns.

Q: What is a real-world example of the CET1 capital ratio? In the worked example, a large US bank reporting a 12.0 percent CET1 ratio actually fell below its all-in minimum of 12.5 percent when you add the G-SIB surcharge and stress capital buffer. That triggered MDA restrictions on dividends and bonuses even though the headline ratio looked healthy.

Q: How can investors use the CET1 capital ratio? Compare reported CET1 to the bank's disclosed all-in requirement, which includes the conservation buffer, G-SIB surcharge, and stressed capital buffer. The gap between reported CET1 and the all-in minimum is the buyback capacity. A shrinking gap limits returns to shareholders.

Q: How is the CET1 ratio different from book equity divided by total assets? Book equity uses total assets in the denominator; CET1 uses risk-weighted assets. Because low-risk assets like Treasuries carry near-zero risk weights, a bank's RWA can be far smaller than its balance sheet. A bank with 8 percent book equity ratio could easily report a 15 percent CET1 ratio.

Sources

1. Basel Committee on Banking Supervision. "Basel III: A global regulatory framework for more resilient banks and banking systems." Bank for International Settlements. https://www.bis.org/publ/bcbs189.pdf
2. BIS Financial Stability Institute. "The capital buffers in Basel III, Executive Summary." https://www.bis.org/fsi/fsisummaries/b3_capital.pdf
3. BIS Financial Stability Institute. "Overview of Basel III and related post-crisis reforms, Executive Summary." https://www.bis.org/fsi/fsisummaries/b3_rpcr.pdf
4. Federal Reserve. "Stress Tests and Capital Planning." https://www.federalreserve.gov/supervisionreg/stress-tests-capital-planning.htm

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.