Two Australian inflation gauges are out today — here's which one the RBA really follows

The quarterly trimmed mean is likely to move the Australian dollar and front-end yields more than the monthly headline number. A quarterly core print of 1.0% or above would exceed the pace implied by the RBA’s August forecasts and raise the odds of a rate increase at the November 2 and 3 meeting. A weaker underlying result would allow the RBA to stay patient even if fuel costs keep the headline rate elevated. Whenever the monthly and quarterly headline readings differ, the first market reaction can be unwound as traders disregard the top-line figure in favour of the core gauge. Energy prices remain the key to headline inflation, so oil will determine how strong the monthly number looks in coming months.

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Earlier:

• Australia CPI preview: banks see 1.0% core rise, above the RBA’s 0.8% forecast

• Economic and event calendar in Asia Wednesday, October 28, 2026. AUD CPI, RBA and RBNZ

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Australia’s monthly CPI may now supply the headline number, but the quarterly trimmed mean is still the RBA’s preferred gauge, which makes it the important release today.

Summary:

• The two releases — September’s monthly CPI and the September quarter CPI — are scheduled for 00:30 GMT, or 20:30 US Eastern on Tuesday and 11:30 in Sydney.
• Since November 2025, the ABS has put out a full monthly CPI covering most of the basket each month, in place of the partial Monthly CPI Indicator.
• The monthly CPI is now the headline measure of inflation and the yardstick for the RBA’s 2% to 3% target; the quarterly figure is simply a three-month average.
• For underlying inflation, the RBA continues to rely on the quarterly trimmed mean, while monitoring the newer monthly measures as their seasonal patterns are still evolving.
• Major banks see the quarterly trimmed mean near 1.0% on the quarter and 3.6% on the year, ahead of the roughly 0.8% quarterly pace built into the RBA’s August forecasts; headline is estimated near 1.3% on the quarter and 3.9% on the year.
• September’s monthly headline is expected to rise to around 4.2% on the year. When price pressures build over the quarter, the monthly reading can sit above the quarterly rate.

The two data points are the September monthly CPI and the September quarter CPI, and market participants need to understand the distinction before reacting. The ABS will issue both at 00:30 GMT, 20:30 US Eastern on Tuesday or 11:30 in Sydney.

Before late 2025, the official Australian inflation measure was the quarterly CPI, while the monthly release was only an indicator. That older Monthly CPI Indicator refreshed prices for just about half the basket each month, with many services priced once a quarter, so it was uneven and volatile. It was followed by markets, but the Reserve Bank of Australia regarded it as a rough guide.

November 2025 brought the shift, with the ABS publishing a complete monthly CPI for the first time using October 2025 data. Prices for most goods and services are now gathered every month, drawing on web-scraped online prices, transaction records and government data, and the series is adjusted for seasonality. The monthly CPI now carries the main headline-inflation role, and its annual rate is assessed against the RBA’s 2% to 3% target.

The quarterly CPI remains in existence. It is built from the monthly figures, with the quarterly index based on the average of the three months, and it appears alongside the monthly data in the March, June, September and December releases. So the quarterly headline has been overtaken in importance and is now a by-product of the monthly series rather than an independent survey.

The quarterly release still matters, mainly because of underlying inflation. The RBA’s long-standing preferred gauge is the quarterly trimmed mean, which excludes the quarter’s biggest price rises and falls to expose the core trend. The central bank continues to treat that quarterly measure as its main underlying gauge, frames its forecasts in quarterly trimmed mean terms and keeps an eye on the newer monthly measures as well. The monthly trimmed mean has a track record of only about 18 months, and with seasonal patterns still developing it can be noisier. The RBA wants to move to monthly measures as they become established, while the ABS has promised to produce the quarterly series until at least 2027.

That is why today’s quarterly trimmed mean is the figure most likely to drive markets and affect the RBA’s November 2 and 3 meeting. Australia’s major banks broadly expect it to gain about 1.0% on the quarter and about 3.6% year on year, faster than the roughly 0.8% quarterly pace in the RBA’s August forecasts. On the headline side, quarterly CPI is projected to rise about 1.3% on the quarter and 3.9% year on year, while September’s monthly CPI is expected at about 4.2% year on year, up from 4.0%.

The two top-line readings do not conflict. The monthly rate compares September with the same month a year earlier, while the quarterly rate compares the average of July, August and September with those same three months a year earlier. When inflation is increasing over the quarter, the monthly figure rises above the quarterly figure, which is exactly what forecasters predict for this release.

For traders, the working rule is that the monthly headline sets the mood, but the quarterly trimmed mean remains the decisive RBA gauge, at least until the monthly measures have earned comparable trust.