Australia will publish its August consumer price index on Wednesday, September 30, at 01:30 GMT, corresponding to 21:30 US Eastern time on Tuesday, September 29. The report arrives one day after the Reserve Bank of Australia raised its cash rate by 25 basis points on Tuesday, September 29, and traders will be looking to the numbers for guidance on what the central bank may do next.

Forecasts point to a faster headline rate. Annual CPI is expected to rise to 4.0%, up from 3.5% in the prior reading. On a monthly basis, prices are forecast to increase 0.4%, a slower pace than the 1.0% recorded previously. That combination suggests the annual figure is being driven at least in part by comparisons with earlier months rather than by a fresh surge in prices, although the forecasts alone cannot confirm that. Australia's monthly CPI is compiled by the Australian Bureau of Statistics as a partial indicator, drawing on a subset of the consumer basket, so the quarterly release remains the fuller measure of price trends; the monthly figures nonetheless give markets their most frequent read on inflation.

The key forecasts at a glance:

• Release timing: Wednesday, September 30 at 01:30 GMT (21:30 US Eastern on Tuesday, September 29)
• Headline CPI: 4.0% year-on-year forecast, versus a prior of 3.5%
• Monthly CPI: 0.4% forecast, versus a prior of 1.0%
• Trimmed mean: 3.6% year-on-year forecast, unchanged from the prior; 0.3% month-on-month, versus 0.5% previously
• Policy backdrop: follows the RBA's 25 basis point cash rate increase on Tuesday, September 29

The trimmed mean measure is the one policymakers tend to watch most closely for underlying pressure, because it strips out the most extreme price movements. Here the forecasts are steadier. A result in line with expectations would show underlying inflation holding at an elevated level rather than accelerating.

The outcome matters because the RBA has just tightened. A reading at or above forecast, especially in trimmed mean, would lend support to the argument that further tightening could be needed. A softer outcome would give the market reason to question that path. The distinction between the headline and underlying figures is likely to shape the reaction, since a headline beat alongside a trimmed mean miss would send mixed signals.

The Australian dollar is the most direct read-through. A print at or above forecast would strengthen the case for further tightening and could support the currency and short-dated yields, which track expectations for the near-term policy path and tend to respond first to inflation surprises. A softer result, particularly in trimmed mean, would invite doubts about how far the central bank needs to go. Because the RBA has already moved, the data now shapes expectations for the next decision rather than the last one. For oil, the relevance is indirect, through the Australian dollar and broader risk sentiment.

Both the forecast headline and trimmed mean rates remain above the Reserve Bank of Australia's 2%–3% inflation target band. Investors will next look to the RBA's communication and subsequent data releases — the quarterly CPI among them — to judge whether the latest increase is the start of a sequence or a single adjustment.

Source: ForexLive — Australia CPI preview: headline inflation seen at 4.0% after RBA hike