Australia swapped its inflation benchmark for one with 18 months of history

Australia changed the instrument it uses to measure the cost of living on 26 November 2025, and the change is larger than a move from four readings a year to twelve. The Australian Bureau of Statistics published a complete monthly Consumer Price Index for the October 2025 reference month, retired the partial Monthly CPI Indicator it had run since September 2022, and made the new series the primary measure of headline inflation. The Reserve Bank of Australia adopted it as the benchmark variable for the inflation target the same month.

The rebuild was substantial. The CPI basket is divided into 87 expenditure classes. In April 2024 the ABS began pricing many more of them every month, and in its information paper of 18 November 2025 it reported that about 44 of the 87 classes changed collection frequency. Under the old design, 50 per cent of the basket by weight was priced monthly, 41 per cent quarterly and 9 per cent annually. Under the new design 87 per cent is priced monthly, 4 per cent quarterly and 9 per cent annually. Roughly 67 per cent of transport and 62 per cent of furnishings and household equipment moved to monthly pricing.

New data replaced old estimates. Child care prices had been modelled; Services Australia now supplies an anonymised census of about 500,000 fee and subsidy payment records each month. Insurance premiums, once collected from insurers directly, come from a third party supplying about 40,000 premium prices a month. Apartment prices, previously carried forward between quarterly observations, are now interpolated. Web scraping and transaction records fill other gaps.

The cost sits in seasonal adjustment. In a technical note dated 4 November 2025, the Reserve Bank's Economic Analysis Department set out the problem plainly: standard seasonal adjustment of monthly data requires at least three years of history, and 46 per cent of the basket by weight had monthly series beginning only in 2024. For 15 per cent of the basket the ABS backcasts a longer series before adjusting it. For 10 per cent it smooths the unadjusted numbers where movement looks seasonal. For 21 per cent it assumes little or no monthly seasonality. The note warned of residual seasonality and of further revisions when standard techniques become available from April 2027. Because the trimmed mean is calculated from seasonally adjusted data, the Bank's preferred underlying measure inherits the problem, and the Bank said it would keep leaning on the older quarterly trimmed mean during the transition. The ABS agreed to keep publishing seasonally adjusted quarterly data on the pre October 2025 collection basis for at least 18 months.

Australian Statistician David Gruen conceded the limit on the day of the first release, telling the ABC on 26 November 2025 that for about half the basket the agency had only 18 months of data. That first reading put annual inflation at 3.8 per cent for October 2025, up from 3.6 per cent in September, with electricity up 37.1 per cent over the year. Economists read it as hawkish. EY chief economist Cherelle Murphy said a rate rise might even be considered.

The measurement change reaches people who never read a statistical release. On 30 October 2025 the Australian Office of Financial Management told holders of Treasury Indexed Bonds that a quarterly CPI would continue, now calculated as the average of three monthly CPIs, and that from the December 2025 release published on 28 January 2026 all index numbers would be re-referenced to September 2025. Period to period percentage changes "may differ slightly to those previously published due to rounding and the re-referencing", the AOFM said, adding that "these differences do not constitute a revision". The quarterly CPI is the number written into indexation clauses across leases, contracts and payments.

The distributional gap is measured elsewhere and less often. The ABS Selected Living Cost Indexes for the June quarter 2026, released on 5 August 2026, showed age pensioner households facing 4.7 per cent annual cost growth and other government transfer recipients 4.6 per cent, against 3.7 per cent for employee households and a headline CPI of 3.8 per cent for the twelve months to June 2026. Within the quarter the pattern inverted: employee households rose 1.5 per cent, the fastest of the five groups, as mortgage interest charges climbed 8.2 per cent on the back of cash rate increases. Those indexes remain quarterly. The households whose costs diverge most from the headline still wait three months for a number.

Wages are set against the headline regardless. On 2 June 2026 the Fair Work Commission announced its Annual Wage Review decision, lifting modern award rates 4.75 per cent and the national minimum wage 6 per cent from 1 July 2026, and said it had aimed to leave award reliant employees no worse off in real terms than on 1 July 2025.

What is not known is how much of the inflation recorded since November 2025 was seasonal noise the interim adjustment methods failed to remove. The ABS cancelled its mid 2026 weight update after concluding household spending patterns were stable, moving the next to January 2027. The test arrives in April 2027, when standard seasonal adjustment can be applied across the basket and the history is revised. Until then nobody can say whether the readings that shaped 2026 will survive contact with the corrected series.