The S&P/ASX 200 Index (ASX: XJO) was down 0.1% at 11:30am AEDT today.
That's when the Australian Bureau of Statistics (ABS) released the latest batch of inflation data for the September quarter.
In the minutes that followed the ABS release, the ASX 200 dropped like a stone. At the time of writing, the benchmark Aussie index is down 0.8% for the day.
Why is the ASX 200 crashing on the September inflation data?
The ASX 200 came under heavy pressure after the ABS reported that the Consumer Price Index (CPI) indicator rose 1.3% in the September quarter and 3.2% annually, significantly outpacing market expectations.
Commenting on the unexpectedly high inflation print, Michelle Marquardt, ABS head of prices statistics, said, "The CPI rose 1.3% in the September 2025 quarter, which is the highest quarterly rise since March 2023."
She noted that the largest contributor to price rises was electricity costs, which increased by 9% over the three months.
As for the rise in annual inflation, Marquardt said, "This is the highest annual inflation rate since the June 2024 quarter when annual inflation was 3.8%."
And no Aussies will be spared the higher costs, with food prices up 3.1% over the September quarter.
"Food inflation continues to be elevated due to higher prices for meals out and takeaway foods, up 3.3% compared to 12 months ago," Marquardt said.
She added, "Other notable price rises over the past 12 months included the 14.6% rise for coffee, tea and cocoa. This reflects lower supply from major overseas suppliers of coffee beans."
The overall picture here greatly dims the odds that ASX 200 investors will see an interest rate cut from the Reserve Bank of Australia. The RBA meets again next week on 4 November to deliver its next interest rate decision.
The RBA delivered its second rate cut of the year on 12 August, bringing the official Aussie cash rate to 3.60%. The central bank left rates on hold at its 30 September meeting, citing concerns over sticky inflation.
Those concerns now appear to have been well-founded.
What about trimmed mean inflation?
ASX 200 investors and mortgage holders alike will also be tuning into the latest trimmed mean inflation print. That's the metric favoured by the RBA in making its interest rate decisions.
The ABS notes, "When prices for some items move by large amounts, measures of underlying inflation like the trimmed mean can give more insights into how inflation is trending."
Unfortunately, trimmed mean inflation is also heading the wrong way.
According to Marquardt:
Trimmed mean annual inflation was 3.0% to the September quarter, up from 2.7% to the June quarter. This is the first time trimmed mean annual inflation has increased since December 2022.
Despite today's dip and ongoing concerns over inflation and elevated interest rates, the ASX 200 remains up 9.1% year to date.
