Inflation data today will likely determine whether the Reserve Bank will cut interest rates 45 minutes before the Melbourne Cup next Tuesday.

The Consumer Price Index (CPI) is expected to have risen 0.5 per cent in the September quarter for an annual rate of 1.1 per cent, according to an AAP survey of 14 economists.

Underlying inflation, which strips out the effects of volatile price movements, is forecast to have been at 0.4 per cent in the quarter and 1.6 per cent over the year.

Both annual figures sit below the central bank's two to three per cent target band.

The Reserve Bank has been eagerly awaiting the September quarter inflation data to assess the impact of its two rate cuts this year on consumer prices.

Commonwealth Bank senior economist Michael Blythe said an underlying inflation reading of 0.3 per cent or less today would leave inflation at low levels forecast ahead of this year's rate cuts.

He said reading of 0.6 per cent or above would indicate inflation was returning to target quicker than expected. Mr Blythe said that left a grey area in the 0.4-0.5 per cent range in the inflation print where next week's interest rates decision would be a judgement call by the RBA board. "The RBA's inflation projections published in August suggest headline inflation will be lower than the Bank expected but underlying inflation will be on track," he said in a note.

"A central bank concerned about low inflation and the risk to inflation expectations may then cut. But a central bank worried about housing, debt and financial stability may leave interest rates alone."

The central bank has relieved borrowers and upset savers on race day in the past: the RBA cut interest rates just 45 minutes before great race on November 2, 2011.

The September inflation quarter data will be released today by the Australian Bureau of Statistics.

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