The calculator uses Consumer Price Index (CPI) inflation data from the Office for National Statistics from 1988 onward. Monthly calculations of the current year are based on the latest CPI level, whereas previous years use their calendar year averages. CPI estimates before 1988 are modelled based on data collected for the Retail Price Index (RPI).
The calculator uses the Consumer Price Index (CPI) as this is the measure used by the Government to set the Bank of England’s target for inflation. An alternative credible measure, which is the ONS’s lead measure of inflation, is the Consumer Price Index including Owner Occupiers’ Housing Costs (CPIH).
Please note: the estimates in the calculator from 1949 onwards have been updated with revised CPI estimates from the ONS published in May 2022.