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".