In 1820, the islands of present-day New Zealand had a population of approximately 100,000 people. This figure would fall until the early 1840s, partly as a result of European diseases brought by colonizers, and a series of destructive inter-tribal wars among the Māori peoples. These conflicts were named the Musket Wars due to the European weapons whose introduction instigated the conflicts, and the wars saw the deaths of between 20,000 and 40,000 Māori, from 1807 to 1837. After falling to just 82 thousand in the 1840s, the population would begin to rise again in 1841 following the establishment of New Zealand as an official British colony, with a strong promotion of European settlement by British citizens sponsored by the Church of England. European migration to New Zealand was low in these early decades, but increased in the mid-19th century, particularly following the discovery of gold in New Zealand’s South Island in the 1860s. This growth would continue throughout the 1870s, in part the result of a strong promotion of mass migration from Britain by Premier Julius Vogel’s administration.

Early 20th century However, between 1881 and the 1920s, the New Zealand government heavily restricted Asiatic migration to the islands, resulting in a fall of population growth rate, which would remain until the Second World War. The country would experience a dip in population during the First World War, in which New Zealand would suffer approximately 18,000 military fatalities, and another 9,000 lost to the coinciding Spanish Flu epidemic. The population would stagnate again in the Second World War, which resulted in the death of almost 12,000 New Zealanders. In the years following the war, New Zealand would see a significant increase in population due to the mixture of a baby boom and a migrant spike from Europe and Asia, following a large demand for unskilled labor. Recent decades This increase continued for several decades, until international factors, such as the oil crises of 1973 and 1979, and the UK's accession to the European Economic Communities (which ended most of New Zealand's trade agreements with Britain; it's largest trade partner), greatly weakened New Zealand's economy in the 1970s. As a result, population growth stagnated during the 1970s, while economic problems persisted into the early 2000s. In contrast, the Great Recession of 2008 did not impact New Zealand as severely as most other developed nations, which allowed the economy to emerge as one of the fastest growing in the world, also leading to dropped unemployment levels and increased living standards. In 2020, with a population of almost five million people, New Zealand is regarded as one of the top countries in the world in terms of human development, quality of life and social freedoms.

In New Zealand, the crude birth rate in 1850 was 37 live births per thousand people, meaning that 3.7 percent of the population had been born in that year. This rate fluctuates over the next thirty years, reaching it's highest recorded number in 1870 (42.3 births per thousand), before dropping consistently from 1880 until 1935. In 1935, New Zealand's crude birth rate was just 17.4 births per thousand people, however New Zealand then experienced a relatively large baby boom after the Second World War, and did not fall to it's pre-war level again until the late 1970s. From the 1980s onwards, New Zealand's crude birth rate has remained around the mid-teens, although it is expected to fall to a record-low of 12.6 births per thousand in 2020.

Life expectancy in New Zealand was just over 34 in the year 1870, and over the course of the next 150 years, it is expected to have increased to just over 82 by the year 2020. Although life expectancy has generally increased along a gradual curve throughout New Zealand's history, there was a slight dip in the late 1910s, as a result of the First World War and following influenza epidemic. Apart from this, there were no anomalies that reduced life expectancy throughout this 150 year period.