CPI

The Consumer Price Index (CPI), catalogue 6401.0, is Australia's main measure of inflation for metropolitan households. It covers residents of 8 capital cities, from Sydney to Canberra, as a weighted average of the 8. The Australian Bureau of Statistics compiles it under the Consumer Price Index Manual 2020. It tracks 87 expenditure classes with about 800 elementary aggregates per city and about 6400 price samples nationally. It is not a cost of living index. It excludes rural households, land, house prices and mortgage interest.

Prices are collected through the reference month, with each item priced in the same week each month. Results appear on the last Wednesday of the next month at 11.30am Canberra time. Quarterly averages join the March, June, September and December issues with extra tables. Each release brings a media release, time series tables and analytical series. These include the seasonally adjusted index, the Trimmed mean and the Weighted median. Original indexes change only to fix a major error, while adjusted series update each month. Markets read annual and monthly percentage moves for policy and for indexing pensions, benefits, rents, wages and contracts.

11 groups drive the index, with weights referencing December 2024.

• Housing, 21.39%: shelter and utilities including rents and new dwelling purchases.
• Food and non-alcoholic beverages, 17.44%: groceries and eating out.
• Recreation and culture, 12.74%: holidays, entertainment and recreational goods.
• Transport, 11.45%: motor vehicles, fuel and fares.
• Furnishings, household equipment and services, 8.02%: furniture, appliances and household services.
• Other groups: Health 6.73%, alcohol and tobacco 6.58%, insurance and financial services 5.58%, education 4.69%, clothing and footwear 3.25% and communication 2.13%.

In the March quarter 2024 release of 24 April 2024, the index rose 1.0% for the quarter and 3.6% over the year. That was down from 4.1% in the December 2023 quarter. It was the fifth straight quarterly fall since the 7.8% peak in the December 2022 quarter. The Trimmed mean was 4.0% over the year, down from 4.2% and below its 6.8% peak, after rising 1.0% in the quarter. The Weighted median rose 1.1% in the quarter. The largest rises were rents at 2.1%, secondary education at 6.1%, tertiary education at 6.5% and medical and hospital services at 2.3%. School fee resets lift each March quarter while rents add steady pressure, and the core above the headline shows slow underlying cooling.

1. Split spending: yearly totals for 87 classes come from household surveys and national accounts, split into fine product lines with scanner data.
2. Build the sample: outlet types match shopping shares, with 3 specialty stores for each department store where shares are 75 to 25. The same item is repriced while it stays typical, with pure quality change removed.
3. Move each small group: divide each price by its base to get relatives, and average with a geometric mean where items substitute. For 28 classes, multilateral methods weight full transaction records.
4. Update the basket: apply each move to past spending totals to price the fixed basket now, then sum to class, group and total levels. For illustration, an 8000 basket rising to 8123 moves by 8123 less 8000 over 8000 times 100, which equals 1.5%.
5. Average the cities: add city totals at each level, so the 8-city mean move gives the national change as weights shift with prices.
6. Do the index math: the index equals the past index times current over past totals, with moves from rounded scores to 1 decimal place. The base is September 2025 at 100.00, weights rest on 2023-24 spending and December prices, forming a Lowe fixed-quantity basket. Index levels print to 2 decimal places.
7. Adjust for seasons and core: test all 87 classes for seasons and refresh factors each month. The Trimmed mean drops the top and bottom 15% by weight and averages the middle 70%. The Weighted median is the move at the 50th rank.