Revisions and correction of errors policies for consumer price inflation statistics: December 2025

Consumer price inflation statistics are important indicators of how the UK economy is performing. They are used in many ways by individuals, government, businesses and academics. Inflation statistics affect everyone, as they influence interest rates, tax allowances, benefits, pensions, savings rates, maintenance contracts and many other payments.

As consumer price inflation statistics are used in indexation it is imperative that every effort is made to ensure all data are included in the first release of any month's figures to avoid the need for revisions and correction of errors in published statistics.

Being clear, transparent and consistent with revisions and correction of errors is important as it manages users' expectations and informs published statistics' appropriate use. This approach also ensures that we are proactively meeting the Code of Practice for Statistics.

The Office for National Statistics (ONS) has a central Revisions and Correction of Errors Policy, which applies generally to ONS's statistics, analysis and data. However, consumer price inflation statistics have specific revisions and correction of errors policies, which apply to the Consumer Prices Index including owner occupiers' housing costs (CPIH), Consumer Prices Index (CPI) and Retail Prices Index's (RPI) published statistics. This is because consumer price inflation statistics are used in adjusting values, such as fees, charges or incomes. Index-linked gilts, pensions, rail fares and commercial contracts all rely on these statistics for adjustments.

The Consumer Price Inflation Statistics Revisions Policy and Correction of Errors Policy are stated separately to clearly highlight the differences between them. Within each policy there is information on:

• how the policy is applied

• in what circumstances users will be notified

• how users will be notified

This Policy replaces and supersedes our previous Revisions policy for consumer price inflation statistics, published in March 2017.

Revisions are updates to previously published statistics, analysis or data that improve quality by incorporating improved methods, additional data sources or statistics that were unavailable at the point of initial publication.

Revisions should not be confused with the correction of errors; revisions are not published to correct a mistake.

Occasionally, consumer price inflation statistics are re-referenced. Re-referencing refers to a rescaling of the indices so that they equal 100 for a given year. Re-referencing is considered a revision only if it affects published inflation rates.

CPIH and CPI Revisions Policy

Our standard practice for the Consumer Prices Index including owner occupiers' housing costs (CPIH) and Consumer Prices Index (CPI) is to not revise when methodological improvements are introduced. Both CPIH and CPI would only be revised in situations where the update is in the public interest. This is because consumer price inflation statistics are put to many uses, most notably indexation. These uses mean that consumer price inflation statistics are market sensitive, and it is imperative that every effort is made to ensure all data are included in the first release of any month's figures and that revisions are avoided.

The CPIH has been revised twice since its launch in 2013. The first revision was on 24 March 2015, which incorporated improvements to the measurement of owner occupiers' housing costs (OOH). The second was on 21 March 2017, incorporating Council Tax and revised weights for OOH. In both cases, the full back series (to 2005) was revised. Both revisions were made before CPIH gained accredited official statistics status.

The CPI has been revised twice since its introduction in 1996. The first revision occurred in 2000, when the final version of the international classification system for analysing results was adopted and earlier indices were reworked onto the new basis. The recalculation resulted in occasional revisions. This was generally no more than plus or minus 0.1 index percentage points to some of the sub-indices and the overall index.

The second revision to the CPI was in 2006 when it was re-referenced from 1996 to 2005 equals 100. As mentioned previously, re-referencing is not normally considered a revision. However, in this instance, revisions were made as the method of calculating derived statistics, such as rates of change, was changed from one based on published rounded indices to unrounded indices. Both revisions to CPI occurred before official statistics in the UK were defined and regulated by the Statistics and Registration Service Act 2007. This act established the UK Statistics Authority as the oversight body.

At the time of writing, we do not expect to make further revisions to CPIH or CPI. However, if revisions are required, users would be alerted to any updates through our monthly Consumer price inflation statistical bulletin.

RPI Revisions Policy

Once published, the Retail Prices Index (RPI) is never revised because of user expectations and because it is widely used for indexation. Revising the RPI could have significant financial and legal implications for pensions, index-linked government bonds and contractual commitments.

Despite having quality control measures in place, mistakes may be found in our statistics. Corrections of errors are amendments made to published statistics in response to mistakes identified after initial publication. Identifying and notifying users of errors is an important part of transparency, which helps to sustain public confidence in line with the Code of Practice for Statistics.

Corrections should not be confused with revisions. Corrections address mistakes, whereas revisions incorporate improved methods, additional data sources or statistics that were unavailable at the point of initial publication. Errors may occur from not carrying out the calculations correctly, where we have identified that a method we have applied was incorrect, or if there was an error in the input data.

CPIH, CPI and RPI Correction of Errors Policy

Errors in published headline consumer price statistics

Where incorrect data have been identified and the discrepancy exceeds 0.1 percentage points from the headline Consumer Prices Index including owner occupiers' housing costs (CPIH), Consumer Prices Index (CPI) and Retail Prices Index (RPI) annual growth rate publications, a public correction will be issued via a correction notice. If multiple errors have been identified within a single month and the cumulative discrepancy exceeds 0.1 percentage points, this will also be reported through a correction notice. These identified errors are reported at the top of the affected release in a blue collapsible banner titled "Correction notice". This acts as a note on the publication that an error has been identified and includes details on the nature of the mistake. This is in line with the central Revisions and Correction of Errors Policy.

Where an error in a published statistic is identified and the discrepancy does not exceed 0.1 percentage points from the headline annual growth rate's accurate value, the error will not be highlighted at the top of the release via a correction notice. The rationale for this is that the consumer price inflation statistics series is published rounded to one decimal place [note 1] and as a result we will only issue a correction notice for errors that exceed this threshold. Cumulative errors that exceed 0.1 percentage points solely through the accumulation of multiple errors below this threshold across months will not be reported via a correction notice. This is consistent with our users' needs and expectations.

In both these scenarios to provide additional clarity, the next published index following an error will feature a description of the error in an appropriate section within the bulletin if affected, or through notices on the affected tables. Irrespective of whether the 0.1 percentage point threshold is met, data in the original publication will not be amended to reflect the correct data. This is consistent with international guidance from the International Labour Organization (ILO) and other national statistical institutes (NSIs), including Statistics Canada.

The following month's published index will be calculated using the corrected information in both these scenarios. However, the historical index data in this release, which details previously published statistics, will not be corrected, as our policy is to only correct errors going forwards. We do not backdate corrections to avoid potential financial and legal disputes where consumer price inflation statistics have been used in indexation.

Errors in aggregation tables and supplementary microdata releases

As well as the headline consumer price inflation publications, we also publish aggregation tables and supplementary microdata. Aggregation tables are published to the Classification of Individual Consumption According to Purpose's (COICOP) subclass (five-digit) description level. These aggregation tables include indices to three decimal places. However, the data in aggregation tables published to three decimal places are not accredited as official statistics.

Where incorrect data have been identified in aggregation tables or supplementary microdata publications, the releases will not be amended. A correction notice will only be issued if an error, or the cumulative discrepancy of multiple errors within a single month's data for an individual consumption segment series, calculated without rounding, exceeds 0.1 percentage points. No correction notice will be issued if the unrounded error or errors are less than 0.1 percentage points.

A correction notice for errors in aggregation tables or microdata releases will not be usually be issued in the headline consumer price inflation statistics publications. The rationale for this is that errors in aggregation tables and supplementary microdata do not usually impact the headline consumer price statistics to the 0.1 percentage point annual growth rate's discrepancy threshold outlined previously.

The aggregation tables and supplementary microdata featured in the following month's published index will include the correct information and a description of the error in an appropriate section, for example, through notices on the affected tables. The index history in this publication will not be corrected as we only correct errors going forwards.

[1] We also publish consumer price inflation statistics series to three decimal places for secondary users.

Indexation

The process of adjusting values, such as fees, charges or incomes, based on changes in a reference price index. This is commonly done to account for inflation and maintain purchasing power over time, or to ensure that tax liabilities are appropriately adjusted to reflect changes in asset values.