NAB, ANZ Lead Mortgage Complaints Among Big Five Banks

ASIC-reported data shows NAB and ANZ recorded the highest mortgage complaint rates among five large Australian banks over the year to the second half of 2025.

Updated on Nov. 15, 2026 in Banking

Flat-color vector editorial illustration of five brass house keys fanned across a cream surface in mustard and coral, one key raised above the rest. — NAB and ANZ recorded the highest mortgage complaint rates among five large Australian banks over the year to the second half of 2025, according to ASIC data. AI Illustration. Upload story photo >

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NAB and ANZ recorded the highest mortgage complaint rates among five large Australian banks, according to an analysis of ASIC's publicly reported internal dispute resolution data. Combined complaint volumes across the five banks were largely unchanged over the year to the second half of 2025.

Why it matters

The analysis measures complaints against mortgage account numbers, allowing comparison between banks of different portfolio sizes. All five banks exceeded the UK mortgage complaint benchmark, a comparison point for mortgage service standards.

Complaint rates were measured per unit measure against the UK mortgage complaint benchmark, with ANZ volumes up 23 per cent and CBA volumes down 28 per cent over the year to the second half of 2025. The analysis does not identify the causes of the divergent trends across the five banks.

The players

Australian and New Zealand Banking Group (ANZ)

ANZ is one of Australia's four major banks, headquartered in Melbourne, and recorded the largest year-on-year rise in mortgage complaints among the five banks examined.

National Australia Bank (NAB)

NAB is one of Australia's four major banks, headquartered in Melbourne, and was among the banks recording the highest mortgage complaint rates in the analysis.

Australian Securities and Investments Commission (ASIC)

ASIC is Australia's corporate, markets and financial services regulator, which publishes internal dispute resolution data and conducted the review of offset account failures.

The details

The analysis compared mortgage complaints across five large Australian banks using ASIC's publicly reported internal dispute resolution data. Separately, an ASIC review of eight banks found that banks paid more than $55 million in compensation for offset account failures between September 2023 and August 2025.

Year to the second half of 2025: combined mortgage complaint volumes across the five banks remained largely unchanged.
September 2023 to August 2025: banks reported more than $55 million in offset failure compensation to ASIC.
15 November 2026: FeedbackIQ published its mortgage complaint analysis.

Market Landscape

Measured against the UK mortgage complaint benchmark, all five Australian banks exceed the reference level in the FeedbackIQ analysis. The comparison places the domestic mortgage complaint picture against an established international yardstick.

Borrowers with mortgages at banks reporting higher complaint rates may want to check how their lender handles disputes and whether their offset account is operating correctly. The analysis highlights that complaint experiences vary considerably between major Australian lenders.

The takeaway

Comparing lenders on complaint data can reveal differences in service that are not visible in headline interest rates. Borrowers can use regulator-published dispute data when weighing where to hold a mortgage.