New KiwiSaver figures confirm fears that women aren't keeping up with men on retirement saving.
More than half of those signed up to the retirement saving scheme are female but Westpac bank, which is the third largest provider, noted in a submission to a KiwiSaver discussion document that balances for women in its scheme are up to 30 per cent lower than men.
The bank found the discrepancy began from the age of 16 and was the greatest for those in their 30s and 40s.
"The greatest discrepancy of 25-30 per cent appears between mid 30s to mid 40s."
Westpac said the discrepancy probably reflected women choosing lower contribution rates than men, having lower average wages and potential career breaks that women may take when looking after children.
The submission raised the issue of the high impact that contribution breaks have on the ability to build up a bigger pool of savings.
Matthew Goldsack, head of investment solutions at Westpac's investment arm BT Funds Management, said it would be a hard ask for women whose balances were so much lower to catch up to men by the age of retirement.
He said an education programme should be run to encourage women to keep contributing the $1042 minimum amount needed to get the $521 annual tax credit even when they stopped working.
Susan St John, co-director of the Retirement Policy and Research Centre at the University of Auckland, said the discrepancy was no surprise and had existed before KiwiSaver.
St John said women were disadvantaged whenever a provision was tied to paid work.
"It is one of the huge dangers that we run in relying on KiwiSaver as opposed to a tax-funded universal scheme which recognises the unpaid work that women do."
St John said the scheme had been good for some women who would not have had access to a work-based retirement scheme before KiwiSaver.
But she said the danger lay in KiwiSaver becoming compulsory and New Zealand Superannuation being relegated by KiwiSaver.
"That is where the big danger is."
David Kneebone, executive director of the Commission for Financial Literacy and Retirement Income, said the retirement savings discrepancy meant women were more likely to face hardship in retirement than men, exacerbated by women living longer than men.
The commission is undertaking a review of New Zealand's retirement income policy this year and one of the six areas it is focusing on is women's future retirement income provision.
"The gap is very obvious - we want to shed light on the subject. Letting things go on as they are is not going to help women in the future."
The review must be completed by the end of they year but Kneebone said he expected to complete it and hand its recommendations to the Government by September.
The research found KiwiSaver had significantly changed the superannuation landscape towards one that is gender neutral but noted that there was a risk that inequality in retirement income could worsen with the increasing significance of KiwiSaver.