Mortgage risk weights – fact check

It is frequently asserted that the major Australian banks have been “gifted” a substantially lower mortgage risk weight than the smaller banks. To be precise, the assertion is that the major banks are only required to hold capital based on a 25% risk weight versus 39% for smaller banks.

If you are not familiar with the arcane detail of bank capital adequacy, then you could be forgiven for concluding that this differential (small banks apparently required to hold 56% more capital for the same risk) is outrageous and unfair. While the risk weights for big banks are certainly lower on average than those required of small banks, I believe the difference in capital requirements is not as large as the simple comparison of risk weights suggests.

Bank capital requirements involve more than risk weights

To understand why this comparison of risk weights is misleading, it will be helpful to start with a quick primer on bank capital requirements. The topic can be hugely complex but, reduced to its essence, there are three elements that drive the amount of capital a bank holds:

1. The risk weights applied to its assets
2. The target capital ratio applied to those risk weighted assets
3. Any capital deductions required when calculating the capital ratio

Problem 1 – Capital adequacy ratios differ

The comparison of capital requirements based on risk weights implicitly assumes that the regulator applies the same capital ratio requirement to all banks, but this is not the case. Big banks are targeting CET1 ratios based on the 10.5% Unquestionably Strong benchmark set by APRA while there is a greater range of practice amongst the smaller banks. Bendigo and Suncorp appear to be targeting a CET1 ratio in the range of 8.5 to 9.0% while the smaller of the small banks appear to be targeting CET1 ratios materially higher (say 15% or more).

If we confine the comparison to the alleged disadvantage suffered by Bendigo and Suncorp, then the higher risk weights they are required to apply to residential mortgages is substantially offset by the lower CET1 target ratios that they target (the 56% difference in capital required shrinks to something in the order of 30% if you adjust for the difference in target CET1 ratios).

Broadening the comparison to the smaller banks gets even more interesting. At face value the much higher CET1 ratios they appear to target suggest that they are doubly penalised in the required capital comparison but you have to ask why are they targeting such high CET1 ratios. One possible explanation is that the small less diversified mortgage exposures are in fact more risky than the more diversified exposures maintained by their larger competitors.

Problem 2 – You have to include capital deductions

This is quite technical I recognise but, in addition to the capital tied to the risk weight, the big banks are also required to hold capital for a capital deduction linked to the difference between their loan loss provisions and a regulatory capital value called “Regulatory Expected Loss”. This capital deduction increases the effective risk weight. The exact amount varies from bank to bank but I believe it increases the effective capital requirement by 10-12% (I.e. an effective RW closer to 28%). My understanding is that small banks are not required to make the same capital deduction.

Problem 3 – The Standardised risk weights for residential mortgages seem set to change

A complete discussion of the RW difference should also take account of the fact that APRA has proposed to introduce lower RW Categories for the smaller banks such their average RW may be lower than 39% in the future. I don’t know what the average RW for small banks would be under these new RW but that is a question you could put to the banks who use the 39% figure without acknowledging this fact.

Problem 4 – The risk of a mortgage depends on the portfolio not the individual loan

The statement that a loan is the same risk irrespective of whether it is written by a big bank or small bank sounds intuitively logical but is not correct. The risk of a loan can only be understood when it is considered as part of the portfolio the bank holds. Small banks will typically be less diversified than a big bank.

Problem 5 – What about the capital required for Interest Rate Risk in the Banking Book (IRRBB)?

I don’t have sufficient data to assess how significant this is, but intuitively I would expect that the capital that the major banks are required to hold for IRRBB will further narrow the effective difference between the risk weights applied to residential mortgages.

Summing up

My aim in this post was not to defend the big banks but rather to try to contribute some of the knowledge I have acquired working in this area to what I think is an important but misunderstood question. In the interests of full disclosure, I have worked for one of the large Australian banks and may continue to do work for them in the future.

On a pure risk basis, it seems to me that the loan portfolio of a large bank will tend to be more diversified, and hence lower risk, than that of a smaller bank. It is not a “gift” for risk weights to reflect this.

There is a legitimate debate to be had regarding whether small banks should be given (gifted?) an advantage that helps them compete against the big banks. That debate however should start with a proper understanding of the facts about how much advantage the large banks really have and the extent to which their lower risk weights reflect lower risk.

If you disagree tell me what I am missing …