What it means
The logic is that a dollar lent is not always a dollar at risk. Cash held at the central bank is close to certain to be repaid, a mortgage secured on a house is fairly safe, and an unsecured loan to a start-up is not, so treating all three the same when setting capital requirements would be crude.
Risk weights scale each exposure to reflect that difference before capital is measured against the total. Weights come from the Basel framework, the international standard that national regulators translate into their own rules.
Under the simpler standardised approach the weights are set by category, while larger banks may use internal models approved by their regulator to estimate risk from their own default and loss data. RWA covers more than lending.
Credit risk is the largest component for most banks, but market risk on trading positions and operational risk covering fraud, systems failure and legal loss are added in as well, and off-balance-sheet commitments such as undrawn credit lines are converted into equivalent exposures and weighted too. For anyone outside banking, RWA explains behaviour that otherwise looks odd.
A bank turning down a profitable loan is often protecting scarce capital rather than doubting the borrower, because a 100% weighted loan consumes far more capital than a government bond of the same size and must earn a return that justifies it. The persistent criticism is that internal models let banks arrive at flattering weights for similar exposures, which is why regulators introduced an output floor limiting how far a modelled figure can fall below the standardised result.
A simple leverage ratio, which compares capital to unweighted assets, sits alongside RWA-based ratios as a backstop.
In practice
Real-world examples.
Example
A regional bank wants to grow its small business lending book by $250 million. Because those loans carry a 100% weight, the finance team calculates that the growth adds $250 million to RWA and requires roughly $27.5 million of extra capital at an 11% target ratio.
Example
A treasurer at a mid-sized bank swaps $150 million of corporate bonds for short dated government paper ahead of a regulatory review. Assets are unchanged, but RWA falls sharply because the government holdings attract a far lower weight, lifting the reported capital ratio.
Example
A commercial borrower is asked to provide property security on a facility it previously held unsecured. The bank explains that the secured structure attracts a lower risk weight, which reduces the capital it must hold and allows a lower margin on the loan.
Think of it
“RWA stands for Risk-Weighted Assets-your assets weighted by their riskiness.
Formula
Calculation
RWA = the sum of each exposure multiplied by its risk weight. Capital ratio = qualifying capital / RWA.
A small bank holds $200 million of cash and government bonds weighted at 0%, $500 million of residential mortgages weighted at 35%, and $300 million of unsecured corporate loans weighted at 100%. Total assets are $1,000 million.
RWA = ($200 million x 0%) + ($500 million x 35%) + ($300 million x 100%) = $0 + $175 million + $300 million = $475 million. So although the bank reports $1,000 million of assets, only $475 million counts for capital purposes.
If the bank holds $57 million of common equity tier 1 capital, its CET1 ratio is $57 million / $475 million = 12%. Shifting $100 million out of government bonds and into corporate lending would add $100 million to RWA, taking it to $575 million and cutting the ratio to roughly 9.9% with no new capital raised.Case study
Seen in the real world.
The following is an illustrative and fictional case. Thornfield Regional Bank, an invented lender, spent three years growing its unsecured business lending because the margins were the best on its menu. Its total assets rose by 20%, but its RWA rose by 38%, and its capital ratio drifted from 13.5% down to 10.4% without anyone treating it as a strategic decision.
When the regulator raised its capital expectation, Thornfield's fictional board faced a choice between raising equity in a weak market or shrinking the book it had just built. The finance team ran a return on RWA analysis for the first time and found that a third of the new lending earned less than the cost of the capital it consumed.
The invented bank repriced part of the portfolio, sold a tranche of loans to an insurer, and introduced a rule that no new facility could be approved without a return on RWA calculation attached. Growth slowed, but capital stopped leaking, and the equity raise was avoided.
Watch out
Common mistakes.
- Comparing two banks by total assets alone, when their risk profiles and therefore their capital needs can differ enormously once weights are applied.
- Assuming a 0% risk weight means an exposure is genuinely riskless, when it reflects a regulatory convention about sovereign debt rather than a guarantee.
- Forgetting off-balance-sheet items such as undrawn overdraft limits and guarantees, which are converted into exposure equivalents and add to RWA.
Questions
People also ask.
Does RWA apply to businesses outside banking?
Not directly, since it is a prudential concept for regulated financial firms, though insurers face a comparable risk-based capital regime.
Why do banks care so much about return on RWA?
Capital is their scarcest resource, so the profit earned per dollar of RWA consumed is a better guide to whether business is worth writing than margin alone.
Can a bank reduce RWA without shrinking?
Yes, by taking security, buying credit protection, selling higher weighted exposures or shifting the mix towards lower weighted assets.
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