Population aged 18 and older in New Zealand - Data and Analysis (1991-2034)

IBISWorld forecasts that the New Zealand population aged 18 and older will rise by 1.4% during 2026-27, to 4,236,800 people. Net migration, which has shifted sharply over recent years, remains the main swing factor behind the year-to-year movement. Even so, the natural growth of the adult population has been underpinned by advances in healthcare and medical technology, which have lengthened New Zealand's life expectancy and kept more people in the cohort for longer.Net migration surged after the removal of international border restrictions in 2022-23, peaking at an annual gain of about 135,500 in the year to October 2023, according to Stats NZ. It has since fallen steeply, easing to roughly 14,200 in the 2025 calendar year, its weakest result since 2013 outside the pandemic. Fewer migrant arrivals, alongside near-record departures of New Zealand citizens, softer domestic labour demand and persistent housing and cost-of-living pressures, drove the decline. Migration began to firm up again late in 2025, steadying the pace of growth among people aged 18 and over through the current year.New Zealand's population continues to age, lifting the share of residents aged 18 and older from around 72% in the early 1990s to an estimated 77.1% in the current year. Over the past five years, this share has held broadly steady, sitting near 77.2% in 2021-22, as strong overall population growth from migration kept pace with the adult cohort. The number of people turning 18 also reflects birth patterns almost two decades earlier, with the relatively high number of births around 2008 continuing to feed the cohort. Overall, IBISWorld estimates the New Zealand population aged 18 and older will grow at a compound annual rate of 1.5% over the five years through 2026-27.