Couples without children are expected to overtake two-parent families as the most common household formation by next year, according to Statistics New Zealand figures.

National Family and Household Projections released today showed the number of families would increase from an estimated 1.17 million in 2006 to 1.46 million in 2031.

Couples without children would account for the majority of the growth, up from 468,000 in 2006 to 721,000 in 2031.

The increasing prevalence of couple-without-children families was mainly due to the large number of people born during the 1950s to the early 1970s reaching older ages, Statistics New Zealand said.

Most of these couples would have had children who had left the parental home.

The figures also showed the number of households would increase faster than the population would grow, with household growth rate projected to increase by an average of 1.2 per cent compared with the population growth rate at an average of 0.8 per cent.

The number of households was expected to reach 2.09 million by 2031, an increase of about 536,000 from June 2006.

"The faster growth in the number of families and households is due to the ageing of New Zealand's population, leading to an increasing proportion of couple-without-children families and one-person households," population statistics manager Bridget Hamilton-Seymour said.