What it means
Banks must hold capital, meaning money put in by shareholders plus profits retained in the business, as a cushion against losses. Rather than demand a flat percentage of every dollar lent, regulators ask banks to weight each exposure by its riskiness first.
Cash and short-dated government debt might carry a 0% weight, residential mortgages 35% to 50%, and unsecured corporate lending 100% or more. The logic is that a bank full of prime mortgages genuinely is safer than one full of speculative property development loans, and the capital rules should say so.
Risk-weighted assets give supervisors a single comparable number across very different balance sheets, and it is the figure sitting underneath headline measures such as the common equity tier 1 ratio. For anyone outside banking, the concept explains why banks price loans so differently.
A facility that attracts a 100% risk weight ties up far more shareholder capital than a mortgage weighted at 35%, and that capital has to earn a return. This is why an unsecured overdraft costs several percentage points more than a secured facility of the same size.
Weights come either from a standardised table published by regulators or from a bank's own internal models, which large institutions may use once supervisors approve them. Internal models tend to produce lower weights, which is why current rules impose an output floor limiting how far a model may undercut the standard table.
The measure has real limits, because a risk weight is a judgement made in advance rather than a measured outcome. Sovereign debt carried a 0% weight through the euro area crisis even as some of it fell sharply in value, a reminder that a low weight does not mean no risk.
In practice
Real-world examples.
Example
A regional bank wants to grow its commercial property book by $200,000,000 at a 100% risk weight. Because that adds $200,000,000 of risk-weighted assets, the finance team calculates it needs roughly $24,000,000 of extra capital to hold its 12% ratio, and the board decides to retain the year's dividend instead of paying it out.
Example
A treasurer negotiating a corporate loan is told the margin will drop by 60 basis points if the company grants security over its receivables. The reason is that security lowers the risk weight the lender must apply, freeing capital that would otherwise sit idle against the exposure.
Example
An analyst comparing two banks sees almost identical total assets but capital ratios of 11% and 17%. Digging into the disclosures, the difference is the mix: one is largely mortgages and government bonds, the other is unsecured lending to small businesses at full weight.
Think of it
“RWA adjusts assets for risk-riskier things count more heavily in capital calculations.
Formula
Calculation
Risk-weighted assets = sum of (exposure amount x risk weight for that exposure)
Capital ratio = regulatory capital / risk-weighted assets
A mid sized bank holds $500,000,000 of cash and government bonds at a 0% weight, $300,000,000 of residential mortgages at a 50% weight, and $200,000,000 of unsecured corporate loans at a 100% weight. The weighted amounts are $0, $150,000,000 and $200,000,000, giving risk-weighted assets of $350,000,000 against $1,000,000,000 of actual assets.
If the bank holds $42,000,000 of tier 1 capital, its capital ratio is $42,000,000 / $350,000,000 = 12%. Measured against total assets instead, the same capital would be only 4.2%, which shows how much the weighting choice changes the picture.Case study
Seen in the real world.
This is an illustrative and entirely fictional example. Harbourgate Bank, an invented mid sized lender, had grown for a decade by writing unsecured loans to small businesses at attractive margins. Management reported a healthy capital ratio each year and saw no reason to change course.
When supervisors reviewed the book, they found that almost every exposure carried a 100% risk weight, so the bank's $4,000,000,000 of assets produced $3,600,000,000 of risk-weighted assets. A rival of similar size, weighted mainly towards mortgages, reported barely half that figure and could therefore support twice the lending on the same capital base.
Harbourgate's fictional board responded by adding a secured lending arm and taking collateral on its larger exposures. Two years later the same balance sheet size produced materially lower risk-weighted assets, and the freed capital funded growth the bank had previously assumed required a share issue.
Watch out
Common mistakes.
- Treating risk-weighted assets as the value of the bank's assets, when they are a regulatory calculation that can be a fraction of, or occasionally more than, the actual balance sheet.
- Comparing capital ratios across banks in different countries without checking whether internal models or the standardised table produced the weights.
- Assuming a 0% risk weight means an exposure is genuinely riskless rather than simply treated that way by the rulebook.
Questions
People also ask.
Why do banks care so much about the risk weight of a loan?
Because capital is expensive, and a higher weight means more shareholder money tied up against the same loan, which directly reduces the return the loan can earn.
Is a lower risk-weighted asset figure always a good sign?
Not necessarily, since it can reflect a genuinely safer book or simply an optimistic internal model, so the ratio should be read alongside the plain leverage ratio.
Does any of this apply to a normal trading company?
Not directly, but it explains bank pricing behaviour, so a business seeking credit can often cut its cost of borrowing by offering security or shortening the term.
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