Childless or empty-nest couples have replaced iconic families of Mum, Dad and the kids as New Zealand's most common kind of household.
Statistics New Zealand's latest family and household projections show that couples without children at home overtook couples with children at home in 2008 for the first time since at least World War II.
Traditional families of Mum, Dad and the kids are projected to shrink further from 31 per cent of all adults aged 18 and over in 2006 to just 23 per cent by 2031.
Couples without children at home are tipped to rise from 30 per cent to 36 per cent of adults, and adults living alone or with flatmates or in other non-family households will rise from 20 per cent to 23 per cent.
Sole parents with children still at home are projected as static at 7 per cent of adults, but the decline in two-parent families with children means the sole-parent share of all families with dependent children will rise from 29 per cent to 34 per cent.
The changes are mainly driven by the ageing population caused by plunging birth rates and death rates over the past 50 years, leading to growing numbers of empty-nesters with no children still at home.
But the lower birth rate, and a rise in the median age of mothers giving birth from 25 in the early 1970s to 30 today, means there are also growing numbers of young adults who have not yet had children - and increasingly never will.
Census figures show that 15 per cent of women who were born in 1965 had not had children by the time they were 40.
Allowing for about 7 per cent of women who are biologically infertile, Statistics NZ experts Bill Boddington and Robert Didham estimated in 2007 that voluntary childlessness increased from less than 1 per cent of women born in 1936 to almost 10 per cent of women born 30 years later.
"For those born just 10 years later in 1975, indications are around one in four may remain childless," they said.
"Studies suggest that few women consciously make the decision to remain childless early in life. On the contrary, deciding not to have children happens as a consequence of other life events, like education, career, mortgages, change in family and partners.
But while two-parent families have declined, sole-parent families rose from 10 per cent of all families with dependent children in 1976 to 29 per cent in 2001.
They dropped back marginally to 28 per cent in the 2006 Census, but Statistics NZ demographer Kim Dunstan said the historical trend towards more sole parents was likely to resume.
Family First spokesman Bob McCoskrie said the projections were a warning shot for the country.
"We should be doing everything we can to promote stable two-parent homes for the sake of the kids, and for the sake of the adults having the support they need to bring up the kids."
But Waikato University demographer Natalie Jackson said trends towards older parenting and fewer children could help more couples stay together in the future anyway.
REASONS TO HAVE BABIES: NONE
For professional couple Sarah Higgins and Murray Harris, there are simply no good reasons to have children.
Ms Higgins, 34, and Mr Harris, 36, both systems administrators for Herald publishers APN, walk to work from their central Auckland townhouse and enjoy the freedom to do whatever they like in their leisure time.
"We want to travel, see some of the world. You can't do that if you have children," Mr Harris said.
Said Ms Higgins: "It's a wonderful thing to be able to say, 'In a month's time we're going away for a week'. We don't have to worry about kids, dogs, cats or anything."
The couple both work 10- or 11-hour days most weekdays and often work at the weekends too.
"So much of our life is work," Ms Higgins said. "I call it selfishness, but I don't know if it is. You worked so hard to get yourself to a point. Am I really willing to bust it all apart?
"The reasons are just not strong enough ... I don't want to live a lifestyle where I'm having to watch every cent."
Mr Harris said the couple's rented townhouse would not be appropriate for children.
"You need to provide a stable environment. That requires home ownership, and that's too expensive. Children themselves are too expensive to raise," he said.
"You go from two incomes to one. Even though we are doing all right, going from two incomes to one income would be hard."
Both, however, have nieces and nephews and enjoy spending time with them.
"You can always be the really cool aunt and uncle, and that way you can give them back when they are hyped up on a sugar rush," Mr Harris said.
"We love kids - just someone else's."