About the CPI Inflation Calculator

• The Consumers Price Index ("CPI") published by Statistics New Zealand ("SNZ") records the change in the price of the "basket" of goods and services purchased by an "average" New Zealand household. The rate of change between the CPI price level today and the CPI price level one year ago is commonly referred to as the inflation rate, or sometimes "headline CPI inflation". Although various other price indices are published by Statistics New Zealand to provide a gauge of inflation in non-household sectors of the economy, the CPI is the most commonly used and recognised measure of inflation in New Zealand.
• Although the rate of inflation is normally thought of in terms of quarterly or annual price changes, it is possible to estimate the inflation that has occurred between two points in time and express this as a percentage change in prices over that period. The Inflation Calculator aims to give people a simple tool for calculating such figures for a selected amount of (New Zealand denominated) money for any two points in time between 1862 and the latest available figure.
• Only partial official CPI data exists between 1914 and 1925. Interpolated figures have been inserted for quarters where no official CPI value is available between these dates. There is no official CPI data available prior to 1914. However, an index of the prices of food and rent, averaged for the four main centres, was once published by SNZ (see Official 1990 Yearbook). Indices for this series have been used for the dates between 1891 and 1913, and linked to the official CPI series beginning in June 1914. Furthermore, in 1911, James W. McIlraith published price indices for general prices (as opposed to consumer prices) from the early 1860s to 1910. We have used this index for the years between 1862 and 1890. It should be noted that the construction of this series is more akin to that of a GDP deflator (covering general rather than consumer prices), so some caution is advised where dates covering this period are entered. These series are not as comprehensive in their coverage as the official CPI and should not be regarded as being of the quality of the official series, but they should provide a fairly reasonable gauge of CPI inflation over this period. For both of these series, a quarterly track has been interpolated from annual estimates and rebased to the current CPI base (June 1999 quarter=1000). For more information on these and other early price data, see Looking at Numbers - a view of New Zealand's economic history, by Phil Briggs, NZIER, Wellington, 2003.
• Note that in using the CPI to measure price changes, the calculator may not give a good estimate of the level of prices of assets (e.g. house prices) or the prices of individual goods/services whose price levels have on average changed by significantly more or less than the change in the CPI in the specified years.
• The "total percentage change" represents the total growth in the price of an average consumer's bundle of goods over the period selected. Also calculated is the average annual (compound) growth rate in prices over the selected years, and the percentage decline (or increase) in the "purchasing power" of the dollar. Where a positive decline has occurred, the Calculator will produce a figure that will be greater than zero and less than 100%. For example, if $1 bought $1 worth of goods and services in 1980 but only 50 cents in 2003 then the purchasing power has declined by 50%. If it only purchases 1 cent worth of goods and services then the decline is around 99%. Where a rise in purchasing power has occurred, it will be expressed as a "negative decline" in purchasing power. This could happen if people enter a current value and want to find out its equivalent value some time in the past. The chart below illustrates the concept, showing the decline in the purchasing power of the NZ dollar since decimalisation in July 1967.
• An article (PDF 78KB) published in the December 2003 issue of the Reserve Bank Bulletin further discusses the functionality of the calculator and gives examples of its uses and limitations.

Disclaimer

The figures produced by the Calculator are offered as guides only and should not be regarded as 'official' Reserve Bank calculations. While every effort is made to ensure that the calculations used to generate the Calculator's outputs are correct, the Reserve Bank will accept no liability or responsibility for any errors or for any use to which the resulting figures may be put. The data used prior to 1914 does not form part of the official Consumers Price Index - the Reserve Bank makes no claims as to the accuracy or reliability of these figures.