GST carve-up change years away: Porter

Western Australian federal Liberal MP Christian Porter insists the prime minister didn't put a time frame on when the government would change how GST revenue is carved up among the states.

In his own mind, Mr Porter - the former WA state treasurer and now social services minister in the Turnbull government - expects it could be several years away.

Mr Porter was at the state Liberal conference last month where Malcolm Turnbull flagged changes to the GST distribution.

"He didn't put any time frame on it, in fact, almost immediately after that announcement I gave some comments to a variety of news outlets noting that in my observation that it would likely be 2019/20 that you would work towards as a target date," Mr Porter said.

WA has suffered under the present GST system which - under the horizontal fiscal equalisation rules - awards jurisdictions which underperform but with a three -year time lag

So while WA has suffered a marked downturn since the mining boom peaked several years ago, it is still receiving less that 30 cents in every GST dollar collected in the state.

He said what Mr Turnbull announced was a policy where there is a floor put in place for what GST revenue a state receives, which is then followed up as relativities change between the states.

"It would mean no state loses out in the out years of its budget cycle, no state would lose a dollar," Mr Porter said.

"For WA the changing relatives moving up are going to take some time."

He said in the long run all states get protected from a situation where states with strong economic growth suffer very big losses in GST.

The WA opposition has repeatedly said Mr Turnbull's pledge to reform the GST carve-up - announced to a cheering audience at the Liberal state conference last month - was aimed at getting the party re-elected in March.

Mr Barnett told parliament on August 16: "The objective of the prime minister is to have that system in place this year."