The inflation rates computed here measure the annual rate of change of the cost of a bundle of goods and services a representative household bought in a base year. In principle, this bundle is the same every year although periodically the bundle is adjusted. The Consumer Price Index (CPI) is used to compute the inflation rate for the United States, and the corresponding, Retail Price Index (RPI) for United Kingdom.

The inflation rate for a particular year is computed by taking the price index of that year minus the price index of the previous year, divided by the price index of the previous year, all multiplied by 100. The result page also give the annualized inflation rate for the entire period from the initial to the ending year.