In general terms, an annual change means the change in the index value in a calendar year relative to the value in the preceding year. Annual changes are calculated by comparing the average of the monthly indices for the whole year with the corresponding averages for the previous year. Annual changes are published in January each year.

Annual changes should not be confused with twelve-month rates of change which specify the development of an index value from one month in a particular year with the same month in the following year.