Childless couples are expected to become the most common family type within three years, according to Statistics New Zealand.
Figures released today show that the number of families is projected to increase by 230,000 or 22 per cent from 1.05 million in 2001 to 1.28 million in 2021.
However, a continuation of recent trends -- lower birth rates, more single parenting and general ageing of the population -- will change the makeup of the average New Zealand family.
Couples without children are expected to number 614,000 in 2021, compared with 407,000 in 2001, an increase of 51 per cent.
While the number of one-parent families is also expected to increase, from 198,000 in 2001 to 251,000 in 2021, the number of two-parent families is set to decline from 446,000 to 418,000.
Meanwhile, the number of households (consisting of either one person living alone or two or more people sharing facilities in a private dwelling) is projected to increase by 380,000 or 26 per cent, from 1.44 million in 2001 to 1.82 million in 2021.
One-person households will increase by 149,000 -- 45 per cent -- from 333,000 to 482,000, largely due to the ageing of the population.
The ballooning number of seniors will also boost the number of people living in non-private dwellings, up 32 per cent from 76,000 in 2001 to 100,000 in 2021.