How we publish our consumer prices outputs

In this article, we explain how we publish and revise consumer price inflation outputs, including:

• Consumer Prices Index including owner occupiers' housing costs (CPIH)

• Consumer Prices Index (CPI)

• Retail Prices Index (RPI)

We outline the release schedule, pre‑release rules, and how corrections are handled. We also summarise the derived statistics we publish, such as growth rates and contributions, and our rounding approach. In addition to the main monthly outputs, we describe supporting tools and data, including microdata, the personal inflation calculator, shopping prices comparison tool, cost‑of‑living analyses, seasonal adjustment work and regional price research. This guidance helps users understand what is published, when it is published, and how to interpret the information.

How we compile measures of inflation

This article is part of a set explaining how consumer price inflation and associated indices are compiled. Other related guidance articles include:  

• Consumer prices indices technical guidance

• Scope and coverage of consumer prices indices

• Traditional data aggregates in consumer prices

• Alternative data aggregates in consumer prices

• Private rents and owner-occupier housing aggregates in consumer prices

• Higher-level aggregation and weights in consumer prices

• Calculating the Retail Price Index

• Special case aggregates in consumer prices

This set of related articles replaces components of our Consumer Prices Indices Technical Manual, 2019. 

The Consumer Prices Index including owner occupiers' housing costs (CPIH), Consumer Prices Index (CPI), Retail Prices Index (RPI) and associated data are issued in our Consumer price inflation, UK statistical bulletin at 7.00am. This is usually published on the second or third Wednesday in the month immediately following the month to which the data refer. In practice, this means publication generally, but not always, falls between the 13th and 21st of the month.

At the same time, accompanying briefing notes are published giving more detail about the factors contributing to changes in the percentage change over 12 months for the headline indices.

The data are also published simultaneously on our website. More detailed data can also be found on our Inflation and price indices web page by downloading the data associated with the latest release as an Excel file or via the time series data function. The latest data are available for download at the same time as the statistical bulletin.

The lower-level consumption segment price indices, price quotes and associated metadata underpinning the production of consumer price statistics are also available in our Consumer price inflation consumption segment indices and price quotes dataset.

In 2016, following an independent review and subsequent public consultation, the then National Statistician published a statement setting out plans for consumer inflation statistics in the UK, to ensure that they meet current and emerging user needs. The Retail Prices Index (RPI) and its subcomponents do not meet the required standard for designation as accredited official statistics. More information on this decision is available in our Calculating the Retail Prices Index article.

In recognition that the index continues to be widely used in contracts, we continue to publish the RPI, its subcomponents, and RPI excluding mortgage interest payments (RPIX). Further detail can be found in our Clarification of publication arrangements for the RPI and related indices article.

In 2020, the UK Statistics Authority (The Authority) and HM Treasury launched a consultation on The Authority's proposal to address the shortcomings of the RPI. From 2030 (at the earliest), as outlined in The Authority's response to the joint consultation on reforming the methodology of the Retail Prices Index, the CPIH methods and data sources will be introduced into the RPI. Additionally, the supplementary and lower-level indices of the RPI will be discontinued.

Choice of publication date

The consumer price inflation statistical bulletin is published as early as is practicable. We aim for publication to take place within four or five weeks following "index day". More information is available in our Traditional data aggregates in consumer prices article.

The choice of publication date needs to consider index day, the time needed to process and quality assure the data, along with the availability of other important input data, such as housing data. The dates of publication are announced in advance on our release calendar. During each summer, the final dates for the following calendar year and provisional dates for the year after that are released.

Pre-release arrangements

On 15 June 2017, the then National Statistician announced that pre-release access to Office for National Statistics (ONS) publications would stop with effect from 1 July 2017, except under exceptional circumstances.

Exceptional circumstances are where someone would need to act or make a decision in the public interest based on the statistics. Not granting pre-release in such a case runs the risk of decisions being made based on out-of-date information. Exceptional, in-confidence pre-release access has been granted to the Bank of England’s Monetary Policy Committee (MPC), solely to inform the Bank’s assessment of the current economic outlook and so the MPC’s monetary policy decision. The dates on which this access is set to occur are published as an exchange of letters between the ONS and the Bank of England.

The Consumer Price Inflation Statistics Revisions Policy and Correction of Errors Policy are presented separately to make clear the distinction between how we handle revisions and how we address corrections. Within each policy, there is information on how the policy is applied, in what circumstances users will be notified and how users will be notified.

CPIH and CPI Revisions Policy

Our standard policy 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. This is in contrast to other ONS statistical outputs, which are covered by the ONS central Revisions and Correction of Errors Policy. 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. 

RPI Revisions Policy

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

CPIH, CPI and RPI Correction of Errors Policy

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 ONS central Revisions and Correction of Errors Policy. Full details are published in the December 2025 update to the revisions and correction of errors policy for consumer price inflation statistics.

Within the consumer prices inflation tables, there are several derived statistics calculated from the underlying indices. These include:

• Growth rates and contributions

• Annual and quarterly averages

• Special aggregates for the Consumer Prices Index including owner occupiers' housing costs (CPIH), Consumer Prices Index (CPI) and Retail Prices Index (RPI)

These derived statistics are published rounded to one decimal point. The effects of rounding are also described in this section.

Growth rates and contributions

Growth rates measure the percentage change in an index between two periods. We publish two growth rates, an annual (or 12-month) change, which looks at the price change over 12 months, and a monthly change, which looks at the price change over the last 2 months. For example, an annual growth rate of 3.5% for the headline CPIH indicates that prices have risen by 3.5% over the past 12 months.

Contributions can be calculated for both monthly and annual growth rates. They show how much each underlying component influences the growth rate, based on their respective price change and expenditure weight. The total sum of contributions adds up to the respective growth rate (either monthly or annual). 

The following is an illustrative example of this calculation, where the individual division level contributions sum up to the total CPIH annual growth rate of 3.5%. 

CPIH annual growth rate: 3.5%

• Division 01 contribution: 1.2 percentage points

• Division 02 contribution: 0.5 percentage points

• Division 03 contribution: 0.2 percentage points

• Division 04 contribution: 0.1 percentage points

• Division 05 contribution: 0.3 percentage points

• Division 06 contribution: negative 0.2 percentage points

• Division 07 contribution: negative 0.5 percentage points

• Division 08 contribution: 0.9 percentage points

• Division 09 contribution: 0.4 percentage points

• Division 10 contribution: 0.2 percentage points

• Division 11 contribution: 0.5 percentage points

• Division 12 contribution: negative 0.1 percentage points

Contributions can aid interpretation of the drivers of inflation. In this example, Divisions 01 and 08 provide the largest upwards contributions, whereas Division 07 is causing a downwards pull on the growth rate.

While the example is given for Divisions, we can also calculate contributions for lower-level aggregates, such as Groups, Classes, Subclasses and Consumption Segments (see Higher-level aggregation and weights in consumer prices)

Contributions to the change in the CPIH or CPI 12-month (annual) rate can also be calculated. For the month of interest, the contribution of each component to the 12-month rate is calculated. The same is done for the preceding month. The differences between the two are the contributions to the change in the rate, which are published in the consumer price inflation statistical bulletin and the accompanying briefing notes.

Growth rates and contributions are calculated when we perform aggregation, and so the detailed methods of how we calculate growth rates and contributions are given in Higher-level aggregation and weights in consumer prices.

In the CPIH and CPI, percentage changes and contributions are calculated from the unrounded indices and are then rounded to one decimal place. However, the RPI is calculated from published rounded indices (see our Rounding policy and the effects of rounding subsection for more detail).

Annual and quarterly averages

The annual average is defined as the arithmetic mean of the 12-month values for the year in question. Quarterly indices (for example, Quarter 1, January to March) are defined similarly. Since the indices are always calculated so that a period (currently the year 2015 in the CPIH and CPI) equals 100, there will not usually be any other year or quarter with an average index of exactly 100.

The CPIH and CPI calculations are performed at maximum precision throughout. In practice, this means that the quarterly and annual average indices are calculated from unrounded monthly indices, with changes over 12 months in the quarterly and annual average indices being calculated from the corresponding unrounded quarterly and annual average indices. The approach adopted in the UK differs from that used in other European countries for each country's Harmonised Index of Consumer Prices (HICP) where:

• annual and quarterly average indices are calculated from the published rounded indices

• the 12-month rates for the annual and quarterly indices are calculated from the unrounded averages of the rounded monthly indices

For consumer price inflation statistics, the annual average inflation rate is the change in the annual average index from the year before. For example, for the all-items CPIH for 2017, we have the annual average equals 103.6, and the annual average for 2016 equals 101.0, so the percentage change is:

In general, this will not equal the average of the percentage changes for January to December but, in practice, the difference will be small. Either average figure will usually be closer to the change between the middle of the year before and the middle of that year than to the change between the start and end of that year.

Note that the Retail Prices Index (RPI) uses a slightly different approach for calculating quarterly and annual average inflation rates. More information is available in our Calculating the Retail Prices Index article.

To calculate an annual average inflation rate over any period other than a full year, the following equation should be used, of which the calculation above represents a special case:

where:

I₂ = CPI or other index in later month or year

I₁ = CPI or other index in earlier month or year

n = number of months in the period in question

It should be noted that this may produce misleading results for just one- or two-months' change in the index. One reason is that the month-to-month change includes a seasonal component. Another is that some prices change only infrequently, perhaps only once a year. So, a comparison between different years' annual average indices, or at least between the same month in different years, is preferred.

CPIH, CPI and RPI special aggregates

For the CPIH and CPI, special aggregates indices include more detailed analysis of goods and services inflation, together with indices calculated by excluding various components from the all-items CPIH or CPI. These indices have been constructed by aggregating together relevant CPIH or CPI classes and using the same principles underpinning the compilation of all other published CPIH or CPI aggregates (as explained in the following subsection). 

A range of special aggregates are also published for the RPI. In 2016, the RPI special aggregates were scaled back to publish only the minimum of RPI-related data necessary to ensure the critical and essential needs of existing users are met. This includes a breakdown by various categories of goods and services, and a selection of indices derived by excluding certain components from the all-items RPI. The latter includes the all-items RPI excluding mortgage interest payments (RPIX), which was the basis for the government's inflation target until December 2003.

How to construct aggregates (after 2015)

For the CPIH and CPI, the indices for Classification of Individual Consumption According to Purpose (COICOP) divisions, groups and classes can be combined to suit users' requirements where the standard aggregates are not appropriate. In all cases, the weights relate only to the applicable year, not to the whole period since the reference date (2015 equals 100). The aggregate indices must therefore be calculated one year at a time.

Step 1 - for each component, unchain the index for the current month as follows:

• for January, divide the January index by the previous December index and multiply by 100 (this step is needed because both the CPIH and CPI are chain-linked twice each year)

• for February to December, divide the current month's index by the current year's January index and multiply by 100

Step 2 - calculate a weighted average of these indices, using the weights relating to the current year. Note that, from 2017, there are a separate set of weights used for January and for February to December.

Step 3 - to convert the aggregates back to the standard reference base (currently 2015 equals 100):

• the January 2015 index is set to equal 100

• the individual monthly indices between January and December 2015 are then divided by the average of the indices for 2015 and multiplied by 100 to provide an index for each month on the required base, 2015 equals 100

Step 4 - forward indices are then calculated from January 2016 as the inverse of the calculation set out in Step 1.

How to construct aggregates (before 2015)

If chained aggregates prior to January 2015 on the standard reference base (2015 equals 100) are required, they can be calculated in retrospect when the January 2015 index has been calculated:

Step 1 - for December 2014 as 100 divided by the unchained aggregate for January 2015 multiplied by the chained aggregate for January 2015.

Step 2 - for February to November 2014 as the current month's unchained index divided by the unchained aggregate for December 2014 multiplied by the chained aggregate for December 2014.

Step 3 - for January 2014 as 100 divided by the unchained aggregate for February 2014 multiplied by the chained aggregate for February 2014.

Step 4 - for as many years (say, N) as are necessary to get back to the official start of the CPI (January 1996) or CPIH (January 2005). 

Rounding policy and the effects of rounding

All the derived statistics listed above are published rounded to one decimal place. Very occasionally, because of the degree of precision to which decimal fractions are stored electronically, a derived statistic ending with the digit 5 may be rounded downwards. For the main Consumer Prices Index including owner occupiers' housing costs (CPIH), Consumer Prices Index (CPI) and Retail Prices Index (RPI) monthly indices, the percentage changes are manually checked and, where necessary, rounded up if the calculated figure is exactly at the rounding point. Because of practical constraints, other derived statistics are not manually overridden in the same way.

The CPIH, CPI and RPI differ in the way in which the derived statistics are calculated. The CPIH and CPI follow the standard approach, which is to calculate derived statistics from unrounded monthly indices, while the RPI calculations are based on the published rounded indices.

To address this, detailed CPIH and CPI indices rounded to three decimal places are also published in our Consumer prices data tables, although these data are not accredited official statistics and should be used for analytical purposes only.

The RPI approach is transparent in that all derived statistics can be traced back to the published monthly index levels. However, when publishing rounded indices to one decimal place, and then calculating percentage changes from these rounded indices, which are then themselves rounded to one decimal place, some extreme rounding effects can occur. More information is available in our Calculating the Retail Prices Index article.

There are several other outputs produced that can supplement the main inflation publication. Some of these are also updated on a monthly basis, whereas some are less frequent or have been produced as a result of previous research. These include our:

• Consumer price inflation consumption segment indices and price quotes

• Personal inflation calculator

• Shopping prices comparison tool

• a "cost of living" or COLI index

• seasonally adjusted data

• Household final consumption expenditure deflator

• Regional price indices

Consumer price inflation consumption segment indices and price quotes

Our Consumer price inflation consumption segment indices and price quotes dataset provides researchers with access to the detailed underlying data used in CPI, CPIH and RPI production. They are not accredited official statistics and should be interpreted with caution because of sample size and volatility at granular levels.

From March 2026, the introduction of grocery scanner data will lead to changes in what the dataset includes. Our data-sharing agreements with retailers that supply scanner data mean price quote microdata in the dataset will no longer be published for:

• Consumer Prices Index including owner occupiers' housing costs (CPIH) and Consumer Prices Index (CPI) Division 1 (food and non-alcoholic beverages)

• CPIH and CPI Division 2 (alcohol and tobacco)

• equivalent RPI categories

To meet user needs, the ONS will instead publish new aggregate microdata outputs, including regional consumption segment indices and weights, counts of indicator markers, improved average price measures, and distributions of national and regional price levels and price relatives.

We will continue to provide analytical microdata for Divisions 3 to 12 in our price quotes microdataset. There will be no changes to the availability of data in the monthly consumption segment indices dataset.

Personal inflation calculator

How the headline inflation rate affects households depends on which products they tend to spend their money on. Our personal inflation calculator estimates a personal inflation rate based on household spending patterns and compares this with headline inflation. To use the tool, users are asked how much their household spends on a range of categories including:

• groceries

• housing

• transport

• leisure

The calculator will also estimate spending on other areas, based either on the UK average spend, or if a user provides their income, then on average spending for a household on their income level.

The calculator will:

• estimate how much a user's monthly spend has increased over the past year

• shows how this compares with previous years

• break down which items are contributing most to the user's cost-of-living increases

The calculator uses the latest available CPIH inflation indices, but it cannot predict how prices might affect individuals in the future. It also cannot account for any changes in spending habits over time or for variation in prices of products within a category (for example, whether a user buys supermarket own-brand or premium-range groceries).

The interactive provides indicative average spend for each category to allow users to compare their spending with similar households. As of 28 November 2025, the calculation of average expenditures of households with similar incomes has been aligned with the calculation of weights in our Household Costs Indices (HCI) bulletin. This method uses our Living Costs and Food Survey, which provides spending data by income decile for each category. More information can be found in the Household Costs Indices for UK household groups QMI.

For more information about the tool, please refer to the Further information section on the personal inflation calculator page.

Shopping prices comparison tool

Our shopping prices comparison tool is an interactive resource designed to help users understand why their household may have experienced inflation. It illustrates how the average price of a wide range of items has changed over the past year, using the published consumption segment indices and price information we collect monthly.

Users can select from hundreds of items currently included in the consumer prices basket used to produce inflation figures. These items span multiple categories, including:

• groceries

• clothing and footwear

• health

• recreation and culture

• services

• transport

• household items

• eating and drinking out

The tool also displays the current average price for selected items, compared with the same month in the previous year. Average prices are not available for every item. For these items, the tool provides growth rates only.

For more information about the tool, including details on the average price methodology, please refer to the Further information section on our Shopping prices comparison tool page.

A "cost of living" or COLI index

The measures of consumer price inflation are specifically not intended to measure what people often refer to as "the cost of living" although it must be noted that changes in prices will always play an important role in what people understand as changes to their cost of living.

In popular usage, what the "cost of living" means is ill defined. Some use it to mean a measure of the cost of buying sufficient quantities of various items to maintain some minimal standard of living. However, defining this standard is very subjective.

Another definition is an index calculated as at present but restricted to basic essentials. However, it would be difficult to reach a consensus on what constitutes "basic essentials". For example, items such as tobacco could be included or excluded because tobacco may or may not be considered an essential item. Also, many former luxuries, such as telephones are now usually considered essential.

The economic definition of the cost of living is the answer to the question "What is the minimum cost, at this month's prices, of achieving the level of utility actually attained in the base period?". Because of the stress on the minimum cost, a cost-of-living index will usually give a lower rate of inflation than the consumer price inflation indices.

The Office for National Statistics (ONS) previously calculated an approximate superlative index for the UK (PDF, 2.9MB) using the Törnqvist formula for the years 2007 to 2009. Three types of substitution behaviour were set out:

• upper-level substitution (between items) - consumers switch between goods and services, towards those that are becoming relatively cheaper; this can be to a similar product (between apples and pears), or something very different (apples to tablet computers)

• lower-level substitution (within items) - consumers switch between varieties of the same item, for example, between Royal Gala and Golden Delicious apples

• substitution between outlets - consumers switch between shops or type of shop - for example, corner shop to supermarket, or high street to internet

The ONS found that the difference between its superlative index and the Consumer Prices Index (CPI) was larger than that found by other countries that have produced superlative indices. This arises because we have applied the superlative index number formula down to the item level. The approximate COLI measures produced by other countries have typically applied the superlative index formula only at the higher stages of aggregation. This limits the extent to which changes in spending patterns are captured by the indices produced by other countries.

Seasonal adjustment

Consumer expenditure on seasonal items (for example, foods and clothing) can vary substantially over the year. This type of behaviour could be an argument for seasonally adjusting all inflation indices, to adjust for this pattern. However, separate seasonally adjusted measures for the Consumer Prices Index including owner occupiers' housing costs (CPIH), Consumer Prices Index (CPI) and the Retail Prices Index (RPI) are not currently produced for two principal reasons. Firstly, in seasonal adjustment the entry of a new month's data can change the levels data from previous months, as the seasonal pattern is re-estimated. This violates the strict rule of never revising the CPI and RPI. Secondly, not all of the changes are caused by true seasonal patterns. Many are caused by the annual changes in Value Added Tax (VAT) and excise duty, as determined by government, which are not regarded as seasonal effects.

For most uses of the CPIH, CPI and RPI, which involve the annual change in the indices, this pattern has little effect, as changes over twelve months are unaffected. However, any shorter-term comparisons can be distorted by the seasonality.

However, there was increasing interest from users in a seasonally adjusted measure of CPIH and CPI. For this reason, the ONS commissioned a feasibility study on the most appropriate methodology to use in the production of seasonally adjusted consumer prices inflation by the National Institute of Economic and Social Research (NIESR).

The project was successfully handed over to the ONS in 2025, where development work to implement the adjustments is being reviewed. Our ongoing work to review the quality and relevance of our consumer price statistics, including our sampling methodology and measures of accuracy, is described in our Consumer prices development plan article series.

The household final consumption expenditure deflator

The implied deflator for household final consumption expenditure (HHFCE) is sometimes used as a measure of inflation as it affects households. It is different from the Consumer Prices Index including owner occupiers' housing costs (CPIH), Consumer Prices Index (CPI) and the Retail Prices Index (RPI) in both coverage and construction.

The goods and services covered in total HHFCE are as defined by the European System of Accounts (ESA) 2010 and close to that used by the CPIH and CPI. Like the CPIH and CPI, they are classified via Classification of Individual Consumption According to Purpose (COICOP) and like the CPI do not include expenditure on Council Tax. Unlike the CPI, which does not use imputed measures, they include the estimated rent imputed to owner occupiers, which is also a component of the CPIH.

Expenditure by all UK resident households is included whether within the UK or abroad. This contrasts with the CPIH and CPI, which cover spending within the UK, whether by UK or foreign nationals.

The HHFCE deflator, unlike the CPIH, CPI and RPI, is not a pure price index. It is derived (at the end of the estimation process) as the value at current prices divided by the value of the volume measure for the same products, expressed in index number form. In practice, a large number of the indices used to deflate components of HHFCE are compiled from component indices of the CPIH, weighted together to reflect the COICOP. The HHFCE deflator is therefore implicitly a current weighted (that is, Paasche) index whose components are, in large part, CPIH component indices.

The HHFCE deflator is produced quarterly (unlike the CPIH, CPI and RPI, which are published monthly) and is available on our Final consumption expenditure deflator web page.

Regional price indices

There are two types of regional price indices that could be produced: one would measure change in prices over time within a region (a temporal index), the other would measure differences in price levels across regions (a spatial index).

At present, we do not calculate temporal regional price indices. Although it is possible to construct these from the available data sources, the reliability of specific regional components of the data and procedures is generally low. Considerable further development would be needed to ensure that the indices can reliably represent inflation within each of the regions.

Previous work has been undertaken to calculate regional relative consumer price levels (RRCPLs). This work was published in March 2018 in the article Relative regional consumer price levels of goods and services, UK: 2016. RRCPLs provide a comparison of a region's price level relative to the national price level where the UK equals 100. Those regions with an RRCPL above 100 are relatively more expensive than the UK average, while the converse is true for those regions with an RRCPL of less than 100.

For more information on the historical development of regional price indices, please see section 13.8 of Consumer Prices Indices Technical Manual, 2019.

All-items index

An index that is constructed using price indices that represent every type of expenditure within the scope of the consumer price statistic. It is an average measure of the change in the prices of goods and services bought for the purpose of consumption in the UK.

Aggregates

Aggregates (or "strata") are classifications into which the raw data can be separated. The strata "region" and "shop type" within item are generally used for the Consumer Prices Index including owner occupiers' housing costs (CPIH), Consumer Prices Index (CPI), Retail Prices Index (RPI) and the Household Costs Indices (HCIs). The data within each stratum are combined, and the resulting indices for each of the strata are then combined using stratum weights.

Alternative data

These are larger, automatically collected data sources. We have introduced several alternative data sources into the calculation of our consumer price indices since the early 2020s.

Basket

A convenient way to understand the nature of consumer price inflation statistics is to envisage a very large shopping basket comprising all the different kinds of goods and services bought by a typical household. As the prices of individual items in this basket vary, the total cost of the basket will also vary - consumer price statistics measure the change from month to month in this total cost.

Base price

Our index methods measure price change between two months: the base month and the current month. Base prices are the prices that are used to represent the price of a product in the base month. This representative price may be a single sampled price, or an average of many different prices.

Consumption segment

A consumption segment is broader in scope than individual items but is still intended to be relatively homogenous, with respect to price change. 

For example, the consumption segment "rice" includes various representative items, such as dry rice, microwaveable rice, and rice snacks (like rice cakes) from the traditional data collection. For alternative data sources, the consumption segment includes all rice products that have been sold.

In areas of the basket where we are not using alternative data, a consumption segment matches one of our representative items exactly.

Chain linking

A "chain link" is the mechanism we use for connecting indices with different baskets or weights. The calculation relies on a link period (December and January in CPI, CPIH and the HCIs). Subsequent index movements are "chained" to this link period by multiplication.

Class

In the CPIH, the CPI and the HCIs, all categories of expenditure on which significant amounts of money are spent are arranged into 12 divisions, which are subdivided into groups and then into classes. Examples of classes are bread and cereals, water supply, and transport insurance.

We publish price indices for each class.

Coverage

Those transactions that can be identified and measured in practice. This is determined by the expenditure categories for which weights are compiled.

Current price

Our index methods measure price change between two months: the base month and the current month. Current prices are the prices that are used to represent the price of a product in the current month. This representative price may be a single sampled price, or an average of many different prices.

Division

In the CPIH, CPI and HCIs, all categories of expenditure on which significant amounts of money are spent are arranged into 12 divisions, such as clothing and footwear, transport, and recreation and culture.

We publish price indices for each division.

Elementary aggregates

The set of indices calculated at the very first stage of aggregation.

GEKS-Törnqvist

The GEKS-Törnqvist is described as a "multilateral" index method. It uses information from all months within a window, rather than comparing only two months at a time. This allows the index to capture the influence of price movements for products that appear or disappear within the window that may not have been captured by comparing only two months.

Group

In the CPIH and CPI, all categories of expenditure on which significant amounts of money are spent are arranged into 12 divisions, which are subdivided into groups. Examples of groups are food, postal services and insurance.

In the Retail Prices Index (RPI), all categories of expenditure on which significant amounts of money are spent are arranged into 14 groups, such as food, housing and motoring costs.

We publish price indices for each CPIH/CPI and RPI group.

Index day

The specific Tuesday within index week when price collectors collect the majority of prices for traditional data sources. This maximises consistency in month‑to‑month comparisons.

Index week

The designated week, at or near the middle of each month, during which local price collectors gather prices. Index day falls in Index week. 

Items

Any type of consumer good or service that can be purchased, for example, apples. Several different varieties of that item may be available, for example, Granny Smith and Braeburn apples.

Price quotes

Individual prices collected through traditional data collection for specific products or varieties that households buy.

Products

Products, or "varieties", are the varieties of goods or services available within an item specification. For example, automatic washing machines with different specifications are produced by different firms, but they are all automatic washing machines.

Reference period

A price index expresses price levels at a given point in time as a percentage of the level at some previous date, known as the reference period. The level at the reference period is 100.

Representative items

Representative items are those items that are in the basket of goods and services.

Scope

All transactions that one would ideally want to measure.

Section

In the RPI, all categories of expenditure on which significant amounts of money are spent are arranged into 14 groups, which are then subdivided into about 85 sections. Examples of sections are bread, cigarettes, postage, footwear, and rail fares.

We publish price indices for each section.

Traditional data

Prices that are manually collected through traditional sources (in-store, online and by phone). This applies to most areas of the consumer prices basket.

Tukey algorithm

The Tukey algorithm identifies and invalidates price movements that differ significantly from the norm.

Varieties

Varieties, or "products" are the varieties of goods or services available within an item specification. For example, automatic washing machines with different specifications are produced by different firms, but they are all automatic washing machines.

Weight

A factor by which a component is multiplied to reflect the level of consumers' expenditure on that component.