Finance Minister Penny Wong has accused the coalition of dirty tricks on budget costings by using much rosier accrual figures, rather than cash balances.
Shadow treasurer Joe Hockey released interim costings for the coalition's election promises on Wednesday, identifying $31.6 billion of savings over the next four years.
Mr Hockey told reporters the coalition will provide cash figures where appropriate in its final numbers.
"We've taken an accrual approach, there are swings and roundabouts," he said.
But Senator Wong seized on Mr Hockey's reliance on accrual figures, saying it made their figures look "much rosier than they actually are".
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"The difference between cash and accrual bottom lines across the forward estimates is $16.6 billion," Senator Wong said.
"Were federal Labor to use an accrual bottom line, it would be in surplus a year earlier, in 2015/16."
She said it was "a truly remarkable" departure from the rules established by former Liberal treasurer Peter Costello.
"What this means is that Australians will never truly know the state of the budget under a coalition government."
