Opposition finance spokesman Andrew Robb said he stands by coalition “assumptions” as Joe Hockey said claims of a black hole relate to a difference of opinion over calculations.
Mr Robb said he trusted Treasury but didn’t accept that there were some unanswerable questions in the coalition costings.
He said he spent several hours with Treasury officials on Wednesday.
“Out of 304 policies there was established at the end what I would say (was) a difference of opinion on a handful of projects,” he told ABC radio.
“It’s not an error of costings. There is a difference of opinion when you go through the projects that they had identified. We stand by our costings.”
Mr Robb said one such issue related to interest on the multibillion dollar borrowings for the national broadband network, with the opposition calculating a saving of $2.4 billion over the next four years through cancelling the scheme.
However, Treasury calculated that at $1.5 billion, which was described as a $900 million hole.
Mr Robb said the difference related to the interest rate, with the coalition basing its calculation on a 5.5 per cent average of the long-term bond rate over the past six months.
“We said what do you use and they said `We are not telling you’,” he said.
However, Treasury subsequently acknowledged a calculation rate of 4.9 per cent based on a weighted average of other rates that they declined to disclose.
“In the end we agreed to disagree,” he said.
Mr Robb said it was quite legitimate to say there was a difference of opinion and the coalition stood by its costings.
“We have announced $11 billion more savings than Labor because we have said the reckless spending has to stop,” he said.
“Even on the worst case … we are still eight times larger on our surplus than Labor.”
Mr Robb said he had not yet discussed the coalition numbers with independent MP Tony Windsor but had talked to Bob Katter and Rob Oakeshott.
“We were able to take them through the handful of projects which add up to this treasury document,” he said.
“I felt that they saw that what we had done was legitimate.”
Opposition leader Tony Abbott says despite Treasury assertions of a billion dollar hole in its costings, the coalition will deliver budget surpluses.
Mr Abbott said the coalition would deliver substantially larger surpluses than Labor despite the Treasury analysis.
“That is the bottom line of that discussion,” he said.
The opposition leader said there were two competing economic records to think about and Labor’s was one of waste and mismanagement exemplified by the home insulation program, debt and deficit.
“Versus our record of responsible economic management and paying off debt.”