Frequently Asked Questions

The Australian Bureau of Statistics (ABS) will release the first complete Monthly CPI on Wednesday, 26 November 2025. This important release will provide more timely and comprehensive insights into economic conditions experienced by Australian consumers. Below are some questions and answers about the new Monthly CPI.

Why is the ABS moving to a Monthly CPI?

A Monthly CPI represents a valuable addition to Australia’s economic statistics and keeps Australia abreast of global best practice in consumer price data. The move to a Monthly CPI responds to strong demand from government, businesses, economists and the broader community for more timely and frequent data on household inflation. As inflationary pressures can shift rapidly, monthly data provides a more up-to-date picture of prices in the economy and can more quickly detect changes in the trajectory of inflation. This will provide better information for monetary and fiscal policy decisions that have a direct impact on all Australians. Currently, Australia is the only G20 country that does not produce its CPI on a monthly basis.

What does the monthly Trimmed mean tell us?

The Monthly CPI will deliver a more frequent and timely read on inflation. However, monthly data is more volatile than quarterly data because quarterly data smooths out the short-term fluctuations by averaging over three months. The monthly Trimmed mean removes large price movements in either direction and provides a measure of underlying inflation each month. 

Other monthly exclusion-based measures of inflation that can help understand underlying drivers of inflation will also be produced, such as Market goods and services excluding volatile series and All groups CPI excluding particular components series. 

Why do you need to continue to publish the quarterly Trimmed mean?

The Monthly CPI time series is currently a relatively short 18 months. By contrast, the quarterly Trimmed mean has been published by the ABS since 2007 and produced in its current form since 2011 (Underlying Inflation Measures: Explaining the Trimmed Mean and Weighted Median | Australian Bureau of Statistics). 

At the request of the RBA, the ABS will continue producing seasonally adjusted quarterly data, including the quarterly Trimmed mean series, for at least the first 18 releases of the complete Monthly CPI. Continuing to produce the quarterly series will enable users to track developments in this measure of underlying inflation that has been available for 14 years while seasonal patterns in the Monthly CPI become better identified over time.

We have compared the quarterly average of the unpublished monthly Trimmed mean with the published quarterly Trimmed mean movements for the three quarters for which we have data. The outcome is within 0.05 percentage points for each of these three quarters. For further information see Seasonal adjustment for the new complete Monthly Consumer Price Index (CPI).

How long will you publish the quarterly Trimmed mean for?

The Trimmed mean series is derived from seasonally adjusted data. Seasonal patterns can be more effectively detected with a longer time series. There are some monthly Expenditure Classes (ECs) with relatively short time series starting in April 2024. The seasonal factors will mature as the monthly time series lengthens. We will revisit, in consultation with key users, the need to continue publishing the quarterly Trimmed mean in 18 months, at which point we will have 3 years of monthly data.

How are the monthly Trimmed mean and quarterly Trimmed mean different?

The two measures are produced using largely the same underlying data and methods. Differences in their construction include:

• The monthly Trimmed mean will make use of all the monthly price data, whereas the quarterly Trimmed mean uses less price data for around half the CPI basket.
• The monthly Trimmed mean will use monthly seasonal adjustment, whereas the quarterly Trimmed mean uses quarterly seasonal adjustment.
• The monthly Trimmed mean will trim the distribution of monthly price changes, while the quarterly Trimmed mean trims the distribution of quarterly price changes.

Advantages of the monthly Trimmed mean are that it will make use of all the monthly price data and will be published on a monthly basis.

Advantages of the quarterly Trimmed mean are that it uses seasonal adjustment derived from a longer time series and is consistent with the historical quarterly Trimmed mean. These advantages will diminish over time as the monthly time series lengthens.

Will the monthly CPI indicator data be revised back to April 2024 with the Monthly CPI data?

No. The complete Monthly CPI includes additional data to the monthly CPI Indicator. For example, Expenditure Classes that were measured once every three months in the monthly CPI indicator will be measured with prices collected every month in the complete Monthly CPI, starting from April 2024. This will see different monthly movements for these ECs due to the change in price collection frequency. The monthly CPI Indicator data series will cease with the September 2025 month, and the back series will not be revised. The complete Monthly CPI data series will be a new and improved data series commencing on 26 November 2025 with a back series to April 2024.

Will the quarterly series in the complete Monthly CPI be a continuation of the quarterly series currently published by the ABS?

Yes. The new quarterly series derived from the Monthly CPI will be a continuation of the existing quarterly series. There will be an overlap period between April 2024 and September 2025 where quarterly movements that can be derived from the complete Monthly CPI may be different to those already published quarterly. This is due to the increased frequency of price collection in the complete Monthly CPI beginning from April 2024. It’s expected this will result in only small differences in the data at the All groups CPI level. Data for the quarterly CPI published between the June 2024 quarter and September 2025 quarter will not be revised.

How much of the CPI basket is collected monthly compared to the monthly Indicator? 

The following tables show the differences between the collection frequencies of data in the monthly Indicator and the complete Monthly CPI. The complete Monthly CPI will have monthly data for 87% of the CPI basket, compared to 50% of the basket for the monthly indicator. A small number of prices will continue to be collected annually or quarterly in line with when price changes typically happen for those items. This is consistent with international best practice as price collection frequency should align with the likely frequency of change.