One in three middle-aged people who live on their own earn so little they are facing an improvished old age.

Today's recommendation by the interim Retirement Commissioner against increasing the age for NZ superannuation has come with an ominous warning about the need to prepare for retirement.

Peter Cordtz said people's preparedness presented a greater risk to most New Zealanders than the age of eligibility or the level of superannuation.

His recommendation not to raise the retirement age is in stark constrast to the Commission's last three reviews, which argued an increase would match today's longer life expectancies.

He told RNZ's Nine to Noon the real issue was about people's preparedness for retirement.

"Tomorrow's retirees are going to be in much worse shape than today's retirees and I think that's one of the risks in assuming the retirees of today is what they will look like tomorrow," he said.

Retirement expert Susan St John said the recommendation not to increase the superannuation age was sensible, but eligibility based on income should also be assessed.

St John, who is director of the Retirement policy and Research Centre in Auckland, said baby boomers had come into retirement much better prepared than the next generation.

"Many of them benefitted from old-fashioned superannuation schemes, that they've had access to a very liberal, universal NZ Super and that they've been able to work, all sorts of factors have acted to their advantage. They've been property owners and that's been extremely important," she said.

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St John's own research showed that fewer people would reach retirement with a mortgage-free home, with many facing high weekly rental costs as the property market soars.

It also found that 29 percent of people aged between 45 and 64 and living on their own faced income poverty, the second-highest rate behind solo parents.

That was up from 10 percent in 1988.

She said these people had periods in and out of work, had run down their assets, and were reliant on inadequate welfare benefits.

"I think that the Retirement Commissioner is right to say that we need to review the policies that apply to that age group, and in particular in the welfare system, there's some very gray anomalies and injustices in the way that the welfare system works for those that can't work and support themselves in that older pre-retirement category." she said.

St John said she supported the Commission's view not to increase the age of eligibility, but the country was not addressing the elephant in the room - the cost of NZ Super and whether there were better uses for that money.

Last year, NZ Super cost $14.5 billion and that was increasing by more than $1 billion each year. By 2024 it would cost the country nearly $20 billion a year.

St John said the problem was a proportion of that money went to very high income superannuants.

She favoured a universal grant at 65 paid at the net rate of national super, but said there would be a claw back for those earning extra money through working or their investments.

"That money is taxed on a separate scale and that scale is progressive, so that it means that after a point - maybe quite a high point, maybe well over $100,000 - that the effect of that clawback would mean that there was no advantage to having the grant."

"So you would opt to go on the grant and the separate tax rate, or not, at the age of 65," she said.

She said Treasury officials had costed the proposal and it was possible to save between 10 and 15 percent of the annual cost of NZ Super by taking it from people who would not even notice.

Cordtz said what was required was a shift in thinking where broad policy discussions were aligned, something he said the incoming Retirement Commissioner was best placed to lead.