AU CPI explained: what the monthly indicator actually measures

The ABS publishes a monthly CPI indicator and a quarterly CPI. They mean different things. Here's the difference and which one to cite for what.

If you're trying to cite Australian inflation, you have two choices: the monthly Consumer Price Index Indicator (released ~25th of each month) and the quarterly CPI (released ~4th week of the month after quarter-end). They're not the same number. Here's what each measures, when to use which, and why journalists keep mixing them up.

The short version

| | Monthly CPI Indicator | Quarterly CPI |

|---|---|---|

| Frequency | Monthly | Quarterly |

| First released | September 2022 | 1960 |

| Coverage of CPI basket | ~70% (subset of full basket) | 100% (full basket) |

| Components | Mostly goods, some services | All groups |

| Statistical purpose | Timely indicator | Authoritative measure |

| RBA's preferred number | Quarterly trimmed-mean | Same |

| Revisions | Frequent | Rare |

If you're writing a 200-word news brief on "is inflation up or down?", use the monthly indicator for timeliness. If you're a researcher / RBA-watcher building a model or citing inflation in an academic paper, use the quarterly CPI for definitiveness.

Why monthly CPI exists

Until 2022, Australia was the only OECD country publishing inflation only quarterly. That's eternity in financial markets, three months between data points means policy decisions and traders both fly blind.

In 2022 the ABS introduced the CPI Indicator as a monthly companion. It uses a subset of prices (mostly items where the ABS already collected monthly data: food, fuel, alcohol, tobacco, housing rent, electricity, some transport services), then chain-links them to give a monthly inflation reading.

The result is a number that:

Updates monthly (good for sentiment)
Diverges from quarterly CPI by 0.1–0.4 percentage points in any given month (good to know)
Doesn't fully include services prices like healthcare, education, restaurants (because those are surveyed quarterly)

The trimmed-mean and weighted-median

These are not separate measures, they're statistical operations applied to the full CPI basket to get "core" inflation:

Trimmed mean: drop the most volatile 15% of items at each end, then average the remaining 70%
Weighted median: the median price-change after weighting items by basket share

Both are released quarterly only. The trimmed-mean is the RBA's preferred core inflation measure. When the RBA's Statement on Monetary Policy says "trimmed-mean CPI of 4.0%", that's this.

The monthly indicator does not have a trimmed-mean equivalent, there are too few items to trim sensibly.

When to use which (cheat sheet)

| Use case | Use this |

|---|---|

| Tweet "AU inflation in May was X%" | Monthly indicator |

| Headline on Wednesday after release | Monthly indicator (release week) or Quarterly (release week), whichever just came out |

| "What is the RBA looking at when they set rates?" | Quarterly trimmed-mean |

| Academic paper citing AU inflation 2022–2025 | Quarterly headline + trimmed-mean |

| Year-over-year price change for a single category | Whichever frequency the data is available in (varies) |

| Comparing AU to NZ / US / UK | Quarterly headline (other countries' headline numbers are mostly monthly but the BIS aligns on Q for cross-country comparison) |

Programmatic access

from ausdata import Ausdata
api = Ausdata()

# Monthly indicator, last 12 prints
monthly = api.cpi(frequency="monthly", limit=12)

# Quarterly headline, last 8 prints
quarterly = api.cpi(frequency="quarterly", limit=8)

# Trimmed mean
trimmed = api.data("abs", "CPI",
                   filters={"measure": "trimmed_mean", "frequency": "quarterly", "limit": 8})

# Decomposition by group (housing, food, transport, etc.), Wave 2 endpoint
decomp = api.data("abs", "CPI", filters={"by_group": True, "limit": 4})

Common mistakes

Citing the monthly indicator as "trimmed-mean CPI", these aren't the same; the monthly indicator is a different statistical product.
Comparing month-on-month to year-on-year, both are usually quoted year-on-year (i.e. % change vs same month a year ago). Quoting month-on-month "annualised" is a different (and more volatile) number.
Quoting the indicator in week-1 after a release, the indicator gets minor revisions; quarterly CPI rarely does.

What the upcoming ABS changes mean

In 2024 the ABS announced a transition to a fully monthly CPI by November 2025. As of 2026-05, that transition is ongoing, the quarterly publication remains the authoritative cross-checked product, and the monthly indicator covers the timeliness use case.

Both will continue to exist for the foreseeable future. The numbers should converge as more services prices migrate to monthly collection.

TL;DR

Monthly indicator: ~70% basket, timely, slightly noisier
Quarterly headline: 100% basket, authoritative, lags
Trimmed-mean: quarterly only, RBA's preferred core measure
Use the indicator for news and tweets; use quarterly for citation-grade work

Bookmark the ABS CPI methodology page for the canonical reference. Use ausdata.io to skip parsing the SDMX-XML and get the numbers in one API call.