The Five Measures Behind the Inflation Reading

Inflation, for property purposes, is not one number. Inflation (21220) reads five series, each measuring a different part of the same price pressure, standardises each one against its own fifteen-year history, and combines them into a single certified reading. The purpose is to turn “inflation is high” from an impression into a measurement.

The five inputs

1. Headline CPI. The ABS Consumer Price Index for all groups: the whole-basket price level most people see reported. Quarterly, 60 baseline quarters, baseline mean 80.7828. June quarter 2026: 102.31, +2.3236σ.

2. Housing CPI. The housing group within the CPI: rents, the cost of new dwellings bought by owner-occupiers, utilities, and other housing costs such as maintenance and council rates. It is the input most directly tied to the cost of holding residential property and is reported as the node’s primary interpretive input. Quarterly, 60 baseline quarters, baseline mean 77.5118. June quarter 2026: 103.80, +2.5220σ.

3. Trimmed Mean CPI. A measure of underlying inflation: each quarter the ABS removes the items with the largest price rises and falls and measures the rest, so one-off movements do not distort the picture. It is the measure the Reserve Bank watches most closely. Quarterly and seasonally adjusted, 60 baseline quarters, baseline mean 116.3648. June quarter 2026: 146.10, +2.3236σ.

4. PPI House Construction. The ABS Producer Price Index for house construction: what builders pay for materials and labour to build a house. It measures costs before they reach home buyers. Quarterly, 60 baseline quarters, baseline mean 127.8183. June quarter 2026: 182.6, +2.1540σ.

5. Consumer inflation expectations. The Reserve Bank’s published measure of the inflation rate households expect over the year ahead. Quarterly, with a much shorter history: 20 baseline quarters from March 2021, baseline mean 4.7271 per cent. June quarter 2026: 5.47 per cent, +1.2014σ.

From a series to a Z-score

The five inputs are on very different scales: three are consumer price indexes, one is a producer price index, and one is a percentage. To compare them, each is converted to a Z-score: its distance from its own baseline average, measured in standard deviations and written σ. The baseline for every input ends in December 2025; for four inputs it starts in March 2011, and for expectations in March 2021. A Z-score of +2.0σ means the reading sits two standard deviations above that input’s baseline average.

One detail matters for reading these figures. Four of the five inputs are price levels, not rates of change. Their Z-scores say how far prices now sit above their average level over the baseline years, not how fast prices are rising this year. Only the expectations input is itself a rate. The pace of price growth is read separately, from annual percentage changes.

From five Z-scores to one reading

The Codex takes the equal-weighted average of the five Z-scores. Each input carries 20 per cent of the reading, and that average is the node’s certified composite. No single input is the answer on its own. Housing CPI is the most directly relevant to property, but it carries the same weight as the other four.

What the configuration is saying

All five inputs sit above their baseline averages, and four of them are more than two standard deviations above. The composite, at +2.1049σ, is above the two-standard-deviation threshold for the first time in the 22 quarters in which all five inputs are available, and it is the highest reading of those 22 quarters.

Housing CPI reads highest of the five, and housing costs are also rising faster than prices overall: 6.8 per cent over the year to June 2026, against 3.9 per cent for headline CPI and 3.7 per cent for the trimmed mean. Expectations sit lower than the price measures, and because that input’s history begins in 2021, its Z-score is measured against a shorter and more recent window.

Terms worth keeping

Baseline: the fixed window of history each input is measured against, ending December 2025.

Z-score (σ): the distance of a reading from its baseline average, in standard deviations.

Composite: the equal-weighted average of a node’s input Z-scores, the same construction used by Interest Rates (21210).

Certified: a reading formally recorded as the node’s official figure for a quarter.

Price level and rate of change: a price level is where prices stand; a rate of change is how fast they are moving. A price level can sit far above its baseline average while its annual growth is moderate.

Short baseline: a baseline with fewer quarters than the platform’s minimum, disclosed wherever the input is used. The expectations input has 20.

Two Standard Deviation Event: the Codex’s label for a reading beyond ±2σ, a statistically uncommon departure from the baseline average.