Calculating Inflation Rates
Personal inflation calculator & related information
What does this guide contain?
Information on how to calculate your personal inflation rate and how to calculate the percentage change in prices between two periods in time.
How do I calculate my personal inflation rate?
The Retail Prices Index (RPI) is a general purpose measure of inflation based on average expenditure patterns. If you would like an indication of your inflation rates based on your personal expenditure, you can calculate this using the 'Personal Inflation Calculator'.
This will not provide an exact replication of your household's own inflation rate - that would require detailed knowledge of where you shop, the precise purchases you make and the prices you pay. It does however, allow you to input your own typical expenditure patterns across a broad range of items.
The calculator applies these expenditure patterns to average price changes in order to calculate an approximation of your household's particular inflation rate. More information about how the calculator works can be found in the 'Article: Personal Inflation Calculator'.
How do I calculate the percentage change in prices between two periods in time?
Data from table 5.1 or 5.3 of 'Focus On Consumer Price Indices' should be used with this formula:
[(Later date RPI - Earlier date RPI)/ Earlier date RPI]x100
How do I revalue a sum of money?
For example, how do you work out how much maintenance payments or rent has gone up between two dates if these are to be adjusted using the RPI?
Data from table 5.1 or 5.3 of 'Focus On Consumer Price Indices' should be used with this formula:
Sum of money (£) x (Later date RPI/ Earlier date RPI)
How do I calculate inflation rates for the CPI/ HICP?
Data from table 3.1 of 'Focus on Consumer Price Indices' should be used with this formula:
[(Later date CPI - Earlier date CPI)/ Earlier date CPI]x100
Users should be aware that the CPI uses unrounded indices to calculate percentage changes. Therefore, if the published rounded figures in table 3.1 are used in the calculation of rates, the result will not always give the correct value when rounded to one decimal place. If you require unrounded values, please contact the CPI team directly on cpi@ons.gov.uk.
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Consumer Price Indices (CPI) First Release