Basel Capital Requirements: Basel I, II & III Framework

Published: March 17, 2026

Article by Ryan O'Connell, CFA, FRM

Capital requirements are the single most important tool regulators use to keep banks safe. By forcing banks to fund a portion of their assets with equity rather than borrowed money, capital requirements ensure that losses are absorbed by shareholders — not depositors or taxpayers. The Basel Accords, developed by the Basel Committee on Banking Supervision, provide the global framework that over 100 countries use to set these requirements. This guide covers the evolution from Basel I through Basel III, how capital ratios work, and what these rules mean for financial stability. For the broader rationale behind banking regulation and the government safety net, see our guide to Financial Regulation & Deposit Insurance.

What Are Basel Capital Requirements?

Basel capital requirements set minimum levels of equity that banks must hold relative to the risks they take. The goal is straightforward: banks with more of their own money at stake are less likely to take excessive risks and more likely to survive losses without failing.

Risk-Weighted Assets (RWA)

Not all bank assets carry equal risk. A U.S. Treasury bond is far safer than an unsecured consumer loan. Risk-weighted assets (RWA) adjust a bank’s total assets by assigning higher weights to riskier categories. Capital ratios are measured against RWA — not total assets — so that banks holding riskier portfolios must hold proportionally more capital. For example, a bank with $100 billion in total assets might have only $60 billion in RWA if it holds substantial government securities.

Banks report two types of capital ratios: risk-based ratios (capital divided by RWA) and the leverage ratio (Tier 1 capital divided by total exposure, including both on- and off-balance-sheet items). The leverage ratio acts as a non-risk-weighted backstop, preventing banks from appearing well-capitalized simply by assigning favorable risk weights to their assets.

Bank capital is divided into tiers based on loss-absorbing quality:

• CET1 (Common Equity Tier 1) — Common shares and retained earnings. The highest-quality capital, available to absorb losses while the bank continues operating.
• Additional Tier 1 (AT1) — Instruments like contingent convertible bonds (CoCos) that can absorb losses in a going concern but rank below CET1.
• Tier 2 — Qualifying subordinated debt instruments and limited general provisions. Absorbs losses only in liquidation.

Why Capital Matters

A common concern is that higher capital requirements raise banks’ cost of funding and restrict lending. The Modigliani-Miller theorem offers an important counterpoint: requiring more equity does not mechanically raise total funding cost one-for-one, because as leverage falls, equity becomes less risky and shareholders accept a lower required return. In practice, real-world frictions — the tax deductibility of interest and the implicit subsidy from deposit insurance — create a wedge. But the empirical evidence suggests that the effect of higher capital requirements on lending costs is modest, though sudden capital shortfalls can still constrain credit during stress periods.

Basel I (1988)

The original Basel Accord was created by the Basel Committee on Banking Supervision, headquartered at the Bank for International Settlements (BIS) in Basel, Switzerland. It established the first internationally agreed minimum capital standard for banks.

The centerpiece was the Cooke ratio: banks must hold capital equal to at least 8% of risk-weighted assets. The entire framework fit into just 26 pages and assigned assets to four broad risk-weight categories:

Off-balance-sheet activities — such as loan commitments, letters of credit, and derivatives — were converted to on-balance-sheet equivalents using credit-equivalent percentages, then assigned risk weights. For more on how off-balance-sheet activities evolved as the banking industry consolidated, see our guide to banking industry structure.

Basel II (2004)

Basel II was developed to address Basel I’s limitations, expanding from 26 pages to over 500. It introduced a three-pillar structure that remains the foundation of bank capital regulation today.

The Three Pillars

Pillar 1 — Minimum Capital Requirements: Basel II made risk weights more granular, added capital charges for operational risk (fraud, IT failures, legal losses) alongside credit and market risk, and allowed sophisticated banks to use an Internal Ratings-Based (IRB) approach — their own credit risk models — to calculate RWA instead of standardized risk weights.

Pillar 2 — Supervisory Review: Regulators assess the quality of each bank’s risk management processes and determine whether additional capital buffers are needed beyond Pillar 1 minimums.

Pillar 3 — Market Discipline: Enhanced disclosure requirements ensure that investors, counterparties, and the public can assess a bank’s risk profile and capital adequacy, creating market-based pressure for sound risk management.

Why Basel II Failed to Prevent the GFC

Despite its sophistication, Basel II had critical weaknesses exposed by the 2007-2009 Global Financial Crisis:

• Credit rating dependence: The standardized approach relied heavily on credit rating agencies — the same agencies that gave AAA ratings to mortgage-backed securities that later defaulted.
• Procyclicality: Basel II demanded less capital in good times (when measured risk was low but actual risk was building) and more in bad times (when capital was scarce), amplifying the credit cycle.
• No liquidity requirements: Basel II focused entirely on solvency, ignoring the liquidity crises that brought down institutions like Northern Rock and Bear Stearns.
• Limited adoption: In the U.S., full Basel II mainly applied to the largest internationally active banks. Many mid-size banks remained under Basel I rules when the crisis hit.

Basel III (2010-Present)

Basel III was developed in direct response to the failures exposed by the 2008 Global Financial Crisis. It represents the most comprehensive overhaul of bank capital regulation since the original Basel Accord.

The capital conservation buffer (2.5% of RWA) restricts dividend payments and executive bonuses if a bank’s CET1 falls into the buffer zone — creating automatic pressure to rebuild capital. The countercyclical buffer (0-2.5%) is set by national regulators based on credit cycle conditions and released during downturns.

The leverage ratio requires Tier 1 capital of at least 3% of the Total Exposure Measure (which includes both on-balance-sheet assets and off-balance-sheet exposures). Unlike risk-based ratios, it cannot be reduced by assigning favorable risk weights.

Basel III introduced two liquidity requirements: the Liquidity Coverage Ratio (LCR), requiring enough high-quality liquid assets to survive a 30-day stress scenario, and the Net Stable Funding Ratio (NSFR), requiring stable funding sources to match assets over a one-year horizon.

G-SIB surcharges impose additional CET1 buffers on globally systemically important banks, scaled by systemic footprint. The Basel Committee’s global framework assigns G-SIBs to buffer buckets ranging from 1% to 3.5%, but the Federal Reserve’s U.S. methodology (which uses the higher of two calculation methods) can produce surcharges above 3.5%. Under the Fed’s schedule effective October 1, 2025, JPMorgan Chase faces a 4.5% surcharge, while Goldman Sachs and Bank of America each face 3.0%.

Basel III Endgame (Basel 3.1)

The Basel Committee’s 2017 finalization — often called Basel III endgame or Basel 3.1 — introduced the output floor, which requires that RWA calculated using internal models be no less than 72.5% of what the standardized approach would produce. This limits how aggressively banks can use internal models to reduce their capital requirements. The EU began phasing in most Basel III final rules on January 1, 2025, though FRTB market-risk rules are delayed to January 1, 2027. In the U.S., Basel III endgame implementation remains subject to ongoing rulemaking and review.

Stress Testing as a Supervisory Overlay

Stress testing complements Basel’s minimum capital ratios as a Pillar 2-adjacent supervisory tool. In the U.S., the Dodd-Frank Act Stress Tests (DFAST) and the stress capital buffer (SCB) determine bank-specific capital requirements above Basel minimums. The Fed’s annual stress tests model how each large bank would perform under severe economic scenarios, and the resulting SCB is added to the bank’s CET1 requirement. This means two banks with identical balance sheets can face different capital requirements based on their stress test results.

The real-world impact of Basel III has been substantial. Since 2010, major U.S. banks have significantly increased their holdings of high-quality liquid assets, shifted toward longer-term stable funding, and built CET1 ratios well above minimums — major U.S. banks now typically hold 12-15% CET1 compared to the 4.5% minimum.

How to Calculate Basel III Capital Ratios

The four key capital ratios under Basel III are:

Basel II vs Basel III

Basel III was designed to fix the specific failures that Basel II exposed during the Global Financial Crisis. Here are the key differences:

Limitations of Basel Capital Requirements

1. Crude standardized risk weights: Under the standardized approach, a loan to Apple and a loan to a startup both receive a 100% risk weight, despite vastly different default probabilities. While the IRB approach addresses this for large banks, smaller institutions remain constrained by blunt risk-weight categories.

2. Internal models can be gamed: Banks using IRB models have an incentive to minimize modeled risk, which reduces their capital requirements. The Basel III output floor (72.5% of standardized RWA) partially addresses this, but model risk remains a concern.

3. Missing risk categories: Basel does not explicitly capture concentration risk, reputational risk, climate-related financial risk, or cyber risk. As these threats grow, the framework will need to evolve. For how Value at Risk (VaR) models are used in Basel market risk calculations, see our dedicated guide.

4. Residual procyclicality: While the countercyclical buffer reduces procyclicality, it does not eliminate it. Risk weights still tend to rise during downturns as credit quality deteriorates, putting pressure on capital ratios at the worst possible time.

5. International coordination challenges: Different jurisdictions implement Basel at different paces and with national modifications, creating an uneven playing field and opportunities for regulatory arbitrage across borders.

Common Mistakes

1. Confusing capital with reserves. Capital is equity — shareholders’ funds that absorb losses. Reserves are liquid assets held to meet depositor withdrawals. A bank can be well-capitalized but illiquid (plenty of equity but insufficient cash), or liquid but undercapitalized (plenty of cash but too little equity). Basel III addresses both through separate capital and liquidity requirements.

2. Confusing risk-weighted assets with total assets. The 8% capital minimum applies to risk-weighted assets, not total assets. A bank with $100 billion in total assets but only $60 billion in RWA needs $4.8 billion in capital (8% × $60B), not $8 billion. Ignoring risk weighting significantly overstates or understates actual capital needs.

3. Thinking higher capital mechanically restricts lending. The Modigliani-Miller theorem shows that requiring more equity does not raise total funding cost one-for-one — as leverage falls, equity becomes less risky and shareholders accept lower returns. Empirical research confirms modest effects on lending costs from higher requirements, though sudden capital shortfalls during crises can still constrain credit. For more on leverage metrics and the debt-to-equity ratio, see our dedicated guide.

4. Assuming Basel III prevents all future crises. Basel III addresses the specific failures of 2008 but cannot anticipate every future risk. Shadow banking activities, cyber threats, and climate-related financial risks are not fully captured by the current framework. Financial regulation must continually evolve.

5. Thinking the 8% total capital ratio is the binding constraint. Post-Basel III, the binding constraint for most large banks is the CET1 ratio including the conservation buffer, countercyclical buffer, G-SIB surcharge, and stress capital buffer — often totaling 10-12% or higher. The 8% total capital minimum is rarely the constraint that determines bank behavior.