Opposition Leader Tony Abbott insists bringing the budget back to surplus remains a very important priority under a coalition government.
But he can't be precise about the timing because of the "enormous" risks contained in the independent Pre-election Fiscal and Economic Outlook prepared by Treasury and Finance.
"There is a lot of unreliability in the figures," Mr Abbott told reporters on the NSW Central Coast on Tuesday.
"The trouble is we don't know what the starting point is."
Labor has budgeted for a surplus of $4 billion in 2016/17 while the Treasury outlook published on August 13 pointed to a surplus of $4.2 billion.
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Mr Abbott says the outlook should be clear toward the end of the first term of a coalition government, if he becomes prime minister on September 7.
Shadow treasurer Joe Hockey is due to release interim costings of the coalition's election promises when he debates Treasurer Chris Bowen at the National Press Club in Canberra on Wednesday.
Mr Abbott is confident the coalition's "spends and saves" will show a better budget bottom line than Labor's.
"If we are spending less and saving more we will get (to surplus) quicker," he said.
Prime Minister Kevin Rudd said while Labor had been making the big calls on the economy and jobs, Mr Abbott was preparing to cut spending.
"Mr Abbott's priority continues to be cutting jobs, cutting health, cutting hospitals, cutting schools, all to pay for his number one priority, his unaffordable and unfair paid parental leave scheme," he told reporters in Sydney.
Finance Minister Penny Wong says history shows the Liberals cut hard when in power.
When the coalition came to power in 1996 it cut spending by the equivalent of $44.6 billion over two years, or 2.85 per of gross domestic product (GDP) - based on today's figures.
"This is the clearest possible sign of the scale of cuts to come if Tony Abbott is elected. Cutting is in the Liberals' DNA," Senator Wong said in a statement.
University of Queensland economics professor John Quiggin calculates every $10 billion of budget reduces GDP, or economic output, by one per cent and can cost 50,000 jobs.
Shadow finance minister Andrew Robb said Labor was trying to divert attention from its appalling record.
Based on Senator Wong's "fuzzy logic" Labor had cost the economy 780,000 jobs, he added.
"Instead of wasting time mounting pathetic scare campaigns ... Penny Wong would best serve our nation by outlining real plans to actually create jobs," Mr Robb said in a statement.
Senator Wong earlier this year boasted of reducing government spending by $156 billion since 2009.
