In Australia, the '30:40' rule has long served as the primary benchmark for identifying households under mortgage stress. The rule defines a household as being in financial distress if they spend more than 30 percent of their gross income on mortgage repayments, provided they fall within the bottom 40 percent of the income distribution.

However, financial analysts and housing experts are increasingly arguing that this rule of thumb is insufficient for modern economic conditions. The primary criticism is that the indicator is too rigid and fails to account for the nuances of individual household budgets, such as varying levels of non-mortgage debt, cost-of-living pressures, and regional differences in housing costs.

While the 30:40 rule provides a simple metric for policymakers to track broad trends, experts suggest it may mask the reality of many families who are struggling despite technically falling outside the 'bottom 40 percent' income bracket. Furthermore, the reliance on gross income rather than disposable income is cited as a significant flaw, as it ignores the impact of taxation and essential living expenses that have risen sharply in recent years. As interest rates remain a central concern for Australian homeowners, there is a growing consensus that a more sophisticated, multi-factor approach is required to accurately assess the true extent of mortgage stress across the country.