Tony Abbott says he will use Treasury figures as a base for his budget, and that his costings will be "crystal clear" before voters head to the polls.

The announcement marks a changed stance for the Opposition Leader, who has previously expressed distrust for the Treasury figures.

On Tuesday the Treasury and Finance departments will release the pre-election economic and fiscal outlook (PEFO), which examines the state of the budget and the economy.

Mr Abbott says he will use the PEFO as a base for his budget costings as it will be "the best estimate going".

"Hopefully it will be more accurate than previous figures, and we'll obviously be working off the PEFO figures," he told a press conference in Brisbane.

The Coalition has previously said it will not rely on the figures because the forecasts have been wrong in the past.

What is PEFO? Independent pre-election fiscal outlook from the Treasury and Finance departments

Independent pre-election fiscal outlook from the Treasury and Finance departments Established during the Howard era, and falls under the Charter of Budget Honesty Act

Established during the Howard era, and falls under the Charter of Budget Honesty Act PEFO be released within 10 days of the issue of the writ for an election

PEFO be released within 10 days of the issue of the writ for an election It is designed to commit governments to sound economic management

It is designed to commit governments to sound economic management Presents the economic forecasts which underpin expenses, capital and revenue estimates

Presents the economic forecasts which underpin expenses, capital and revenue estimates It includes updated estimates for the current financial year and the next three financial years

It includes updated estimates for the current financial year and the next three financial years It also outlines risks to the budget over the forward estimates

It also outlines risks to the budget over the forward estimates Read more about PEFO on the Finance Department's website.

Earlier this week Mr Abbott said voters could do the math on his costings, and his treasury spokesman Joe Hockey said the Coalition would not provide a final budget position before the September 7 election.

Labor frontbenchers seized on the remarks, with Prime Minister Kevin Rudd saying it showed the Coalition is not "fair dinkum", and Treasurer Chris Bowen saying the Opposition's budget approach revolves around "adding some fairy dust".

But Mr Abbott says the final budget bottom line will be "crystal clear" before the poll.

"All of our policies will be costed and funded, and you will be able to see the net outcome in good time before the election," he said.

"People will have plenty of time to scrutinise what we're spending and what we're saving.

"I've identified more than $17 billion worth of savings, and that's more than enough to cover the carbon tax compensation without a carbon tax, and the company tax cut that are the centrepieces of our plan."

Last week's economic statement released by the Government forecast this year's deficit will blow out by $12 billion to $30 billion and the 2014-15 deficit will more than double to hit $24 billion.

Mr Bowen says Mr Abbott's latest comments show he lacks confidence in Mr Hockey.

"This is yet another position from the Opposition today. More chaos, more disunity, more confusion about how they'll pay for their promises," he told reporters in Sydney.

"Earlier this week the shadow treasurer said that PEFO would not be respected by the Opposition. Today the Leader of the Opposition has said the best estimate going will be PEFO.

"I would like to see Mr Abbott and Mr Hockey being crystal clear with the Australian people about who will cost their promises."