The proportion of couples living without children is increasing and expected to make up more than half the extra 433,000 families expected to be in New Zealand by 2038.
This family type, which also includes couples whose children have left home, will drive the increase in most areas, Stats NZ said today.
New Zealand will have 1.7 million families in 2038 under the mid-range projection.
"While growth in the number of families reflects our growing population, the changing composition of families is driven by our ageing population," said population statistics general manager Peter Dolan. "Many more people will be in the age where their children have left the family home. These are the so-called 'empty nesters'."
Couple-without-children families are the most-common family type in most areas; they are expected to continue to make up the largest proportion of families in almost all areas by 2038.
The exception to the trend is Auckland, where two-parent families are expected to remain the most common broad family type, Dolan said.
"We project that 40 per cent of births in New Zealand will be in Auckland up to 2038, and the region will also receive the lion's share of the country's growth from net migration.
"These factors both contribute to growth in the number of families with children."
However, there is considerable variation within Auckland. The region will continue to be affected by an ageing population, and the number of couple-without-children families is projected to increase by 64 per cent over the 25-year period. The average family size in 2038 ranges from 2.3 in Waitemata, to 3 in Mangere-Otahuhu.
Data projections released today indicate future changes in the number and composition of families and households in New Zealand. Couples, and children living with one or more parents, are examples of "family".