Wealthier Australian families pay a lower rate of tax than poorer families, a new report has claimed.

On average, the effective tax rate for families with assets of $500k-$1m was almost five percentage points lower than families with assets of $100k-$200k, the Productivity Commission estimated in a report released on Wednesday.

“This is mainly due to aged payments and low income taxes paid by the elderly in this group,” the report said.

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These richer households paid an average of 18 per cent tax, including GST, compared to 13.4 per cent for poorer families, according to the commission’s review of the tax and welfare system.

The report estimated effective average tax rates by calculating the total amount of tax paid to the government, subtracting payments to families from the government and dividing that figure by personal income.

The same cohort of wealthier families paid slightly less GST on average, the report found — a difference of 7 per cent of disposable income for families with assets of $100k-$200k, compared to 5 per cent for those with $500k-$1m in assets.

“The reason why GST may be lower as a proportion of expenditure for families with higher ­incomes could be because they are more likely to purchase GST-free items like private education and health services.”

Despite these anomalies, the commission reported that Australia’s tax system is in fact highly progressive, meaning that tax increases as personal income rises.

It was only when wealth, as defined by assets, was compared to tax that inequality was found, and only for some asset brackets.

Debate has raged in Australia of late in the media and parliament on how to make the nation’s tax system fairer and more efficient. The Productivity Commission’s report is a response to this.

The report claimed that if the tax system was not reformed, wealthier Australians would continue to contribute a bigger share of government revenue, resulting in lower levels of disposable income.