The Consumer Prices Index (CPI) and the Retail Prices Index (RPI) measure the changes from month to month in the cost of a representative 'basket' of goods and services bought by consumers within the UK.
This involves weighting together price changes in the indices according to household spending patterns for different categories of goods and services so that each takes its appropriate share.
At the beginning of each year the weights used to compile both the CPI and RPI are updated using the latest available information on household spending.
Here are details of the process for each year shown.
2014 (123.7 Kb Pdf)