The RBA's September commodity price index shows bulk commodity prices up 17.7 per cent over the year, but reading the figure properly means understanding how the index is built and what it leaves out.

Every month the Reserve Bank of Australia (RBA) publishes an Index of Commodity Prices, tracking what the world is paying for the goods Australia digs up, grows and ships. The September 2026 edition, released on 1 October, carried one standout number: bulk commodity prices, measured in spot terms and in Special Drawing Rights (SDRs), were 17.7 per cent higher than a year earlier.

That is faster than the 15.5 per cent annual rise in the overall index in SDR terms. It is also far faster than the 6.6 per cent rise in the overall index when measured in Australian dollars.

Headline figures like these are easy to quote and easy to misread. Below is a practical guide to what the September release actually says, followed by the limits of what it can tell us.

Six things to know about the September index

1. Bulk commodities led the year. The bulk subindex, based on spot prices and measured in SDRs, rose 3.3 per cent in September alone and was 17.7 per cent higher over the year. That outpaced the overall index on both a monthly and an annual basis.

2. The overall index rose too, but less. In SDR terms the full index rose 1.4 per cent in September, up 0.3 per cent in August and 15.5 per cent over the year.

3. The September figure is preliminary. The RBA labelled the 1.4 per cent monthly rise in SDR terms as preliminary. Monthly readings can be revised when later data arrive, so the most recent month is best treated with some caution.

4. Currency matters. In Australian dollar terms the full index rose 1.0 per cent in September and 6.6 per cent over the year. The gap between the SDR and Australian dollar figures reflects movements in the currency, a point explored further below.

5. The rise was broad in September. The rural, non-rural and base metals subindices all rose during the month.

6. Not everything is dearer than a year ago. Iron ore, alumina and copper ore were exceptions to the broad pattern of year-on-year price increases. That matters because a strong subindex reading does not mean every commodity within the index has risen over the year.

Why measure in SDRs at all?

SDRs are the International Monetary Fund's composite reserve unit, and the RBA itself held SDRs worth A$19,318 million among its official reserve assets at the end of September 2026. Measuring commodity prices in SDRs strips out much of the effect of swings in any single currency, including the Australian dollar. That makes the SDR series a cleaner gauge of what is happening to world prices.

The Australian dollar series, by contrast, shows what those world prices are worth once converted into local currency. When the Australian dollar strengthens, the local-currency series rises more slowly than the SDR series, which is what happened over the year to September.

Assistant Governor (Financial Markets) Christopher Kent noted in Sydney on 13 August 2026 that the trade-weighted Australian dollar had risen about 5 per cent since the start of 2026. At 4.00 pm on 9 October 2026 the RBA recorded the currency at US$0.6979 and the trade-weighted index at 64.8.

What the index does not show

The index is a price measure. It is useful, but it has limits that are worth stating plainly:

  • It does not measure volumes. Higher prices tell us nothing on their own about how much Australia is shipping.
  • It does not identify causes. The September release reports price movements; it does not, in the material reviewed here, explain why bulk prices rose.
  • It is not a consumer price measure. The commodity index tracks export prices, not what households pay at the checkout.

That last point is important given the inflation debate. Headline inflation, from the monthly Consumer Price Index (CPI), was 4.0 per cent over the year to the August month of 2026. Underlying inflation was lower: Governor Michele Bullock said on 29 September that "the underlying inflation rate's been about 3.5 per cent for the past six months", and the trimmed mean measure was 3.6 per cent in the June quarter. Both are above the 2–3 per cent target. None of these measures is the same thing as the commodity index.

Where commodity costs do show up in the RBA's inflation story

While the commodity index measures export prices, RBA officials have separately pointed to commodity-related costs feeding into domestic inflation. At her 29 September media conference, Bullock said: "fuel prices, fertiliser prices, transport prices, all these things now are permanently higher."

The Monetary Policy Board's statement that day, announcing a 25 basis point increase in the cash rate target to 4.60 per cent, said higher fuel prices were partly passing through to other goods and services. It also listed further disruption to global oil supply from the Middle East conflict among the upside risks that had materialised.

In Canberra on 18 September, Bullock told the House of Representatives Standing Committee on Economics: "Oil and related prices have increased sharply again and will add directly to inflation."

These comments concern energy and input costs. The facts reviewed here do not say whether or how the commodity index's bulk subindex feeds into those same pressures, so no such link is drawn here.

The bottom line

Bulk commodity prices were 17.7 per cent higher over the year to September 2026 in SDR terms, outpacing the overall index's 15.5 per cent rise, with all major subindices up in the month. But the headline needs context: the September figure is preliminary, iron ore, alumina and copper ore bucked the year-on-year trend, and in Australian dollar terms the overall index rose a more modest 6.6 per cent.

The index measures world prices for Australia's commodities, not household inflation. The next CPI, for September, is due on 28 October, and the next cash rate decision follows at 2.30 pm on 3 November 2026.