Almost a quarter of Australians have completed a bachelor degree or higher, compared to just 8 per cent in 1991, according to new data from the 2016 Census.

The staggering increase has been driven by more students finishing school and the uncapping of university places, which has let institutions recruit as many students as they want since 2009.

But as degrees have become more common, so too has the number of students staying at university for longer to get a competitive edge.

There has been a 46 per cent increase in the proportion of Australians with postgraduate qualifications in the past five years.

The Grattan Institute's higher education program director Andrew Norton raised concerns about the "ever continuing spread of credentialism".

"There are a number of reasons to become concerned," he said.

"It increases the cost to the student in time and money… as bachelor degrees become more common, employers start saying, 'I can screen the CVs I'm receiving by just deleting everyone that doesn't have a particular type of qualification'."

He said that more than half of the Australians with postgraduate degrees were born overseas.

The census data showed that 56 per cent of Australians aged 15 and over, or 9.6 million people, hold a post-school qualification, up from 46 per cent in 2006.

There were also some positive signs for Indigenous Australians. In the past decade, the proportion of Indigenous people with a non-school qualification increased from 25 to 37 per cent.

Federal Education Minister Simon Birmingham, whose landmark higher education reforms have been killed off in the Senate, said the growth in the number of Australians with post-secondary qualifications was paying off.

"Having more highly-skilled Australians helps create more high-skilled opportunities," he said.

Younger women are more likely to hold non-school qualifications than their male peers.

Half of Australia's 20 to 24-year-old women hold post-school qualifications compared to 43 per cent of men.

This has helped narrow the overall gender gap in education levels, with 58 per cent of men and 54 per cent of women holding a non-school qualification.

Qualifications help Australians find jobs and lead to better pay.

More than 80 per cent of those with non-school qualifications aged 20 to 64 were employed, compared with 63 per cent of those without qualifications.

Australians with a bachelor degree or higher took home a median weekly income of $1,436. This compares to $836 for someone with no post-school qualification.

Management and commerce is the most popular field of study, experiencing a 23 per cent growth in the past five years, while society and culture has grown by 29 per cent and information technology by 24 per cent.