"Bro culture" in many workplaces that pay men more than women means that law student Miriam Bookman is entering the workforce with apprehension.

Ms Bookman, 23, is about to sit her final exams for degrees in law and arts at the University of Auckland.

After five years of study she has lined up a legal job in Wellington but will have to repay a $30,000 student loan.

"I'm really not looking forward to that," she said.

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"It doesn't give me comfort that men going into the same job as me, who have the same competency as me, might be paying that off in a shorter time."

The latest Education Ministry report on the student loan scheme says male students who graduated in 2011 will pay off their loans in an average of 6.7 years, but women will take a further six months.

The gap is far smaller than 2005, before student loans were made interest-free. In 2005, men would take an average of 14 years and women 28 years to pay off their debts.

But the fact that the gender pay gap is now widening again may also widen the gap in loan repayment times.

Women are now also leaving study with a slightly higher median debt ($14,070) than men ($13,830).

A 2011 ministry study found that women who finished bachelor's degrees in 2003 and stayed in paid work for the next four years earned the same incomes as equivalent male graduates in their first year of work, but after four years fell 9 per cent behind, averaging $43,380 a year against $47,760 for the men.

Ms Bookman said professions such as law were still male-dominated.

"When you see people climbing the ranks, you see the culture that certain industries maintain," she said.

"I think this is potentially a problem across a fair amount of workplaces that favour bro culture and that sort of thing. I think a lot of this is subconscious, it's not like you walk into an office and you are told who is paid what. It's a behind-the-scenes thing, so it's very hard to pinpoint certain experiences, but certainly it's a real worry."

She said the law should be changed to "give responsibility and direction" on pay, and women needed more information on their rights and on how to negotiate fair wages.