Estimated population of New Zealand

Estimates flagged as provisional are subject to revision, mainly to incorporate revisions to external (international) migration estimates.

https://www.stats.govt.nz/indicators/population-of-nz

The accuracy of the estimates depends on the accuracy of the estimated base and change in numbers. The accuracy of the base depends on the accuracy of the census and the estimated adjustments made to the base.

At URL provided, select 'Population > Population Estimates - DPE > Estimates and Projections: Estimated Resident Population by Age and Sex (1991+) (Annual-Jun). For Estimate Type, only "As at" variable was selected and all remaining other variables were selected to create this dataset.
Figure.NZ calculated the population under 12, 12+ and 5+.

This is an estimate of the number of people who usually live in New Zealand, at a given date. National population estimates give the best measure between census dates of the population that usually lives in New Zealand.
The latest estimated resident population is based on the 2018 Census usually resident population count, updated for residents missed or counted more than once by the census (net census undercount); residents temporarily overseas on census night; and births, deaths, and net migration between census night and the date of the estimate.

All population estimates at 30 June 2018 and beyond use the 2018-base ERP (estimated resident population).