New Zealand's population is projected to reach five million by 2041.
The estimated resident population in June this year was 4.06 million, and much younger than what is predicted for the future.
The projection by Statistics New Zealand is a mid-range estimate assuming New Zealand women will average 1.85 children
from 2016 - down from 2.01 in 2004.
It also assumes life expectancy at birth will improve by about six years by 2051, to 83.5 years for males and 87 for females, and that there will be a net migration gain of 10,000 people a year.
The department's figures show that, under the same scenario, population is expected to slow steadily in the future, mainly because of a large increase in the number of deaths as more people reach old age.
Growth is expected to slow dramatically between 2041 and 2051, with births in 2051 projected to be 8000 fewer than this year's figure of 58,000.
Deaths are projected to more than double between now and 2051 from 28,000 to 59,000.
The statistics show that continued population ageing means about 26 per cent of the population is likely to be over 65 by 2051, compared withonly 12 per cent at the moment.
There will also be six times as many people (320,000) over the age of 85 as there are now.
The statistics also project that seven years from now, the 15-to-39 age bracket will for the first time be out-numbered by those aged 40 to 64.
Only 13 years ago the younger bracket was 56 per cent larger than the older one.
- NZPA
