Retail Price Index
| Month | RPI | RPIX
excluding mortgage interest payments | CPI |
|---|
| December 2022 |
13.4% |
12.9% |
10.5% |
| January 2023 |
13.4% |
12.6% |
10.1% |
| February 2023 |
13.8% |
12.9% |
10.4% |
| March 2023 |
13.5% |
12.6% |
10.1% |
| April 2023 |
11.4% |
10.4% |
8.7% |
| May 2023 |
11.3% |
10.3% |
8.7% |
| June 2023 |
10.7% |
9.6% |
7.9% |
| July 2023 |
9% |
7.9% |
6.8% |
| August 2023 |
9.1% |
7.8% |
6.7% |
| September 2023 |
8.9% |
7.6% |
6.7% |
| October 2023 |
6.1% |
4.8% |
4.6% |
| November 2023 |
5.3% |
4.1% |
3.9% |
| December 2023 |
5.2% |
4% |
4% |
| January 2024 |
4.9% |
3.8% |
4% |
| February 2024 |
4.5% |
3.5% |
3.4% |
| March 2024 |
4.3% |
3.3% |
3.2% |
Introduction
Since the launch of the Consumer Prices Index (CPI) in 1996, there has been considerable interest in the reasons for the differences between the CPI and the Retail Prices Index (RPI) measures of inflation.
The 2010 budget report announced that the CPI will be used for the indexation of benefits, tax credits and public service pensions from April 2011 and the government is also reviewing how the CPI can be used for the indexation of taxes and duties. These announcements have perhaps put the differences between the CPI and the RPI under greater scrutiny than ever before and it is with this in mind that the ONS intends to produce more detailed analyses of these differences for publication in the near future.
Conceptual differences
The historical contexts of the RPI and the CPI are very different.
The RPI began life as a compensation index, developed as an aid to protect ordinary workers from price increases associated with World War 1. It was only much later, after a number of significant developments that it came to be used as the main domestic measure of inflation.
The CPI, which was launched in 1996, is an internationally comparable measure of inflation which employs methodologies and structures that follow international legislation and guidelines. The CPI is the government's inflation target, a target set at 2% since December 2003, when the Chancellor of the Exchequer announced that in future monetary policy would be based on a 'new' measure of inflation - the CPI.
Methodological differences
The basic approach to the measurement of inflation adopted by both the CPI and RPI is the same. Both track the changing cost of a fixed basket of goods and services over time and both are produced by combining around 180,000 individual prices for over 650 representative items.
Differences arise due to coverage, the population base of the indices and the way in which individual price quotes are combined at the first stage of aggregation.