RPI: the Retail Prices Index, where it is still used and its reform

The Retail Prices Index, usually just called RPI, is one of the oldest measures of inflation in the UK. It tracks changes in the cost of a fixed basket of goods and services, including housing costs such as mortgage interest, and it was for many years the most commonly used measure of UK price inflation¹. Today it sits alongside newer measures, CPI and CPIH, but unlike them it is no longer an accredited official statistic: the Office for National Statistics states plainly that "the Retail Prices Index (RPI) and its subcomponents do not meet the required standard for designation as accredited official statistics"³.

RPI is still published every month, because it is written into long-term contracts that affect real money: student loan interest rates, some index-linked savings products, Help to Buy equity loan charges and a range of other financial terms². The annual RPI inflation rate was 3.4% in August 2026⁴, compared with CPI at 3.1% and CPIH at 3.3% over the same 12 months⁵. RPI typically runs higher than the other measures, and from 2030 at the earliest its methods will be brought into line with CPIH, a change that will affect anyone holding an RPI-linked product³.

What RPI is and what it measures

RPI is a measure of inflation, which means it tracks changes to the cost of living in the UK¹. It works by measuring the rise in the cost of a predetermined basket of goods and services, a basket that includes housing costs¹⁰. For many years it was the most commonly used measure of UK price inflation, and its long history is part of why it survives: contracts written decades ago still refer to it¹⁰.

The index is arranged into 14 broad groups of expenditure, covering categories on which significant amounts of money are spent, such as food, housing and motoring costs¹¹. Housing has been treated in different ways over the years: housing depreciation was included in the RPI in 1995 as an element of owner-occupier housing costs². Mortgage interest payments are also part of the picture, which is one reason RPI moves differently from CPI when interest rates change.

Two features of RPI matter most to a consumer. First, it covers only private households, and it excludes the top 4% of households by income and pensioner households who receive at least three-quarters of their income from benefits². Second, the scope and definition of the index is the responsibility of the Chancellor of the Exchequer, not the statisticians who compile it, which is why RPI has been kept largely unchanged even after its methods were found to be flawed². The ONS collects the prices and does the arithmetic, but the boundaries of what RPI measures are set by the Treasury.

RPI inflation now: 3.4% over 12 months

The annual RPI inflation rate was 3.4% in August 2026⁴. That continues a period in which RPI has run above the main official measures: CPI rose by 3.1% in the 12 months to August 2026, up from 2.9% the previous month, and CPIH rose by 3.3%⁵. The Bank of England's own summary puts inflation at 3.1% for August 2026¹².

The recent path shows how the measures move together but not identically. In June 2026 the annual RPI rate was 3.0%¹³, and the July 2026 bulletin reported an RPI rate of 3.2%¹⁴, so August's 3.4% marks a rise over the summer. Within the CPI figures, the all-services index rose by 3.4% in the 12 months to August 2026 while the all-goods index rose by 2.7%, and owner-occupiers' housing costs rose by 3.9%⁴. Core CPI, which excludes energy, food, alcohol and tobacco, rose by 2.6%⁴.

RPIX, the variant of RPI that excludes mortgage interest payments, rose by 3.3% in the 12 months to August 2026⁴. RPIX matters historically because it was the basis of the UK inflation target until 2003, when the Chancellor announced that the target would move to the Harmonised Index of Consumer Prices, the forerunner of CPI². The published RPI index itself stood at 421.6 in the latest figures, on a base of 1987 equals 100, with a 12-month change of 3.4%¹⁵.

How RPI is calculated from the ONS basket of prices

RPI is compiled from the same price collection operation that feeds CPI and CPIH. The sample is based on approximately 760 goods and services, reviewed annually, with prices collected from around 20,000 outlets within the UK². Local price collectors visit 20,000 shops in around 150 locations to collect over 100,000 prices, and around 160 items are collected centrally rather than by local collectors². In total the statistics draw on approximately 180,000 price quotations each month².

The weights, which decide how much each category matters to the overall index, come from household spending surveys: the Living Costs and Food Survey is a continuous survey of the expenditure patterns of private households based on a sample of around 6,000 households per annum². Some categories use large alternative data sources rather than manual collection, including rail fares, second-hand cars and much of the grocery market².

Where RPI genuinely differs is in the arithmetic. Stratum indices are calculated using predominantly the geometric mean for CPIH and CPI, and arithmetic means for RPI at the elementary aggregate level². This is not a technicality: the arithmetic formula is the main reason RPI comes out higher, and it was this formula that the National Statistician concluded in 2013 does not meet international standards². There is a second difference in precision: rates of change for CPIH and CPI are calculated from unrounded index levels, while rates of change for RPI are calculated from the rounded published indices².

All three indices use plutocratic weights, meaning each household's spending influences the index in proportion to how much that household spends¹¹. Price collection usually takes place at a set point in time, the second or third Tuesday of each month, and publication follows four or five weeks later².

RPI and CPI: why the two figures differ

CPI was first published in 1997 as the Harmonised Index of Consumer Prices, a consistent measure designed for international comparison². CPI and CPIH are accredited official statistics; RPI is not². The practical consequence for a consumer is that CPI is the figure used in the government's target for inflation and for uprating state pensions and benefits², while RPI survives in older contracts.

The size of the gap is well established. CPIH has typically been around 0.8 percentage points lower than RPI⁶, and CPI generally increases more slowly than RPI because the indices use different averaging formulae¹⁰. In August 2026 the gap between RPI at 3.4% and CPI at 3.1% was 0.3 percentage points⁴, but over long periods the cumulative difference is much larger than any single month suggests.

Coverage differences add to the gap. CPIH includes owner-occupiers' housing costs and Council Tax, which are excluded from CPI². CPIH measures housing costs using an approach called rental equivalence². RPI, by contrast, includes mortgage interest payments directly, so when interest rates rise, RPI tends to rise relative to CPI, and vice versa. The Household Costs Indices, a separate set of measures designed to show how different household groups experience inflation, include changes in mortgage interest rates, Stamp Duty and other costs related to the purchase of a dwelling, which are omitted from CPI¹⁶.

The Household Costs Indices also show how much these choices matter. In June 2026 the gap between the HCI and CPI annual inflation rates was 0.2 percentage points, and Council Tax, which is not included in CPI, contributed 0.21 percentage points to the HCI annual rate¹⁷. Non-retired households had a higher annual inflation rate in June 2026, at 2.9%, compared with 2.5% for retired households, and over the five years to June 2026 non-retired households and households with children saw cumulative HCI inflation of 33.2%¹⁷. In December 2025 non-retired households again experienced the higher rate, at 3.7%¹⁸. The dedicated pages on CPI and CPIH and the Household Costs Index cover those measures in full.

Where RPI is still used and how it affects you

Although RPI lost its role in government policy years ago, it remains embedded in products and rules that touch ordinary finances. The ONS continues to publish the RPI, its sub-components and the RPIX because they are tied to long-term contracts², and describes RPI as a legacy measure required to meet existing user needs¹⁴.

The clearest everyday examples are:

• Student loans. Interest on English income-contingent loans is tied to RPI in several ways. For Plan 1 loans, the interest rate is the lower of the RPI at the preceding March, or 1% above the highest base rate of a nominated group of banks. For Plan 2 loans, the RPI part of the interest rate is updated once a year in September, using the RPI from March of that year. Borrowers on one repayment plan are charged at RPI plus 3% while studying and throughout repayment, except where a cap applies, and those earning £25,000 or less on another plan were charged at the rate of inflation (RPI)⁷.
• Index-linked savings. NS&I Index-linked Savings Certificates were historically linked to RPI. Instructions to reinvest in an RPI-linked Issue had to be received by 30 April 2019 at the latest; later instructions are linked to CPI, and any Certificates renewed after maturity now have their index-linking calculated using CPI instead of RPI⁸.
• Help to Buy equity loans. Interest on the Help to Buy: Equity Loan scheme (2013 to 2021) is charged at RPI plus 1%¹⁹.
• Some taxes. The Welsh Government's Draft Budget sets out an intention to increase the standard rate of Landfill Disposals Tax for 2026-27 by forecast RPI²⁰.
• Historic benefit uprating. Prior to 2011-12, most benefits were uprated in line with RPI²¹. From April 2011, payments from state benefits, public sector pensions and S2P were indexed to CPI increases instead¹⁰.

Not everything that once used RPI still does. The Pension Protection Fund uprates compensation in line with CPI, not RPI: PPF payments rise in line with the Consumer Prices Index each year, up to 2.5%, and the measure of inflation used by the PPF is CPI²². The wider shift from RPI to CPI for benefits and pensions had real effects: the Office for Budget Responsibility calculated that by 2015-16 the switch had reduced affected rates by 4.4% where they were previously linked to RPI, and 5.9% where they were linked to the Rossi index²⁴. For a person whose income was uprated by CPI instead of RPI, the cumulative difference compounds year after year.

If you hold a product whose terms name RPI, the terms govern: the index written into the contract is the one that applies until the contract changes or the reform arrives. The comparison page CPI or RPI: which inflation measure applies to you works through the common cases.

RPI is no longer an accredited official statistic

RPI's fall from grace was gradual but decisive. In 2013, following a consultation, the National Statistician concluded that one of the formulae used to produce the RPI does not meet international standards, and announced that in future changes to the RPI would be limited to routine changes such as the annual update of the basket of goods and services². In the same year the ONS concluded that the RPI did not meet its required standards for designation as a national statistic²¹.

Since then the position has been stated repeatedly in every consumer price inflation bulletin: the RPI and its subcomponents do not meet the required standard for designation as accredited official statistics³. The ONS's own inflation page labels the RPI series "Not a National Statistic"¹⁵. By contrast, CPIH and CPI are accredited official statistics², and the only UK inflation index designated as an Accredited Official Statistic in the assessment that followed was the CPI²⁵.

The practical meaning for a consumer is about trust and comparability, not availability. RPI figures are still produced monthly with the same collection operation behind them, but the ONS does not vouch for them to the standard it applies to CPI and CPIH, and it advises against using RPI for new purposes. Which? summarised the position when the reform was announced: RPI has been dropped as an official inflation measure by the ONS and is kept as a legacy measure because so many things are still tied to it⁶. The inflation figures page shows which measures carry the accredited status.

RPI reform: CPIH methods from 2030 at the earliest

The reform that will eventually close the gap was agreed following a joint consultation in 2020. From 2030 at the earliest, CPIH methods and data sources will be introduced into the RPI, and the supplementary and lower-level indices of the RPI will be discontinued³. Which? reported the decision as bringing RPI in line with the UK's official CPIH rate by 2030⁶.

The reform is a change of method, not a change of name. RPI will continue to exist and to be published, but it will be calculated using CPIH's methods and data sources, which should bring its published rate down towards the CPIH rate, typically around 0.8 percentage points lower than RPI has been⁶. The discontinuation of supplementary and lower-level RPI indices means some detailed sub-indices that contracts or analysts may have referenced will disappear³.

The date is deliberately cautious. The ONS practice for consumer price inflation statistics is to give advance notice of a minimum of 18 months to a maximum of 30 months for changes², and a change of this scale, affecting long-term contracts, was set further out still. Until the change lands, RPI continues to be calculated as it is now, with the arithmetic formulae that produce its characteristic upward bias².

What the change to RPI means for your money

The direction of the effect is clear: because CPIH methods typically produce a lower rate than RPI methods, anyone whose interest, return or charge is linked to RPI can expect that link to be worth less after the reform than before, once the new methods apply. Which? noted at the time of the decision that the change affects pensions, student loans, rail fares and more⁶.

For borrowers, lower is better. Student loan interest tied to RPI, such as the RPI plus 3% charged while studying on one repayment plan, would fall once RPI is aligned with CPIH methods⁷. The same applies to Help to Buy equity loan interest charged at RPI plus 1%¹⁹. For savers and investors holding RPI-linked products, the effect runs the other way: an index-linked return that grows more slowly than the old RPI would have grown. NS&I has already made an equivalent change for its Index-linked Savings Certificates, switching renewals from RPI to CPI from 2019⁸, which gives a sense of how such transitions work in practice: the terms at renewal, not the original terms, decide.

Two things do not change. First, the reform does not rewrite contracts: it changes the index those contracts reference, so the legal link to "RPI" continues but the number it produces will be lower. Second, nothing happens before 2030 at the earliest³. Anyone with an RPI-linked product has time to check its terms, and the student loans, savings and pensions pages cover the products where RPI most often appears.

Where to find RPI figures and when they are published

RPI is published every month, and the obligation is statutory. Section 21 of the Statistics and Registration Service Act, which came into force on 1 April 2008, stated that the Statistics Authority must "compile and maintain the Retail Price Index and publish it every month"². The figures appear in the ONS consumer price inflation bulletin alongside CPI and CPIH, and the RPI series itself is available as a downloadable time series on the ONS website¹⁵.

The rhythm of the month is fixed. Prices are collected around the second or third Tuesday of each month, and publication takes place four or five weeks later; the ONS notes that publication has never been delayed or missed². Release dates are announced well ahead, with advance notice of a minimum of 18 months to a maximum of 30 months maintained in future years². Recent and upcoming releases illustrate the pattern: the September 2026 consumer price inflation release, carrying the RPI series, was dated 16 September 2026²⁷, and the next release of the series was scheduled for 21 October 2026²⁶.

For the current figures, the ONS consumer price inflation bulletin is the primary source, and the RPI time series pages carry the index values and 12-month changes¹⁵. The latest UK inflation figures page tracks each release, and the wider rates and economy guide puts RPI in the context of Bank Rate, the inflation target and the other price indices.