Federal Treasurer Wayne Swan has ruled out increasing personal income tax, despite having earlier refused to do so.

The Government is coming under pressure to explain how it will pay for key promises, such as the National Disability Insurance Scheme (NDIS) and the overhaul of school funding, given revenue collections have fallen well short of predictions.

Asked repeatedly this morning whether personal income taxes would rise, Mr Swan eventually told ABC Radio National: "I don't... go into that sort of rule in rule out routine, and I'm not doing it today".

"What I'll do is the responsible thing - put in place a strict fiscal policy, make sure that working Australians get a fair go, that there is incentive in the tax system, that we build up their superannuation.

"They're the sort of things I'll do, and I'll leave the speculation for everybody else."

However, he has since released a statement declaring the question to be "utterly ridiculous and absurd".

"The Government's record on personal income taxes couldn't be more clear," Mr Swan said in the statement.

"We delivered cuts to personal incomes taxes in three consecutive Budgets worth a total of $47 billion.

"Last year we tripled the tax free threshold, from $6000 to $18,000, removing around one million people from the tax system."

A spokeswoman for Mr Swan later made clear that personal income tax rises were explicitly ruled out.

Total chaos

Sorry, this video has expired Joe Hockey speaking this morning

Shadow Treasurer Joe Hockey was quick to seize on Mr Swan's earlier comments, declaring the budget was in "total chaos".

"They've got a mining tax that is hardly raising the revenue that they budgeted for, but they spent [it]," he told reporters in Canberra.

"They've now got a carbon tax that is not raising the revenue they budgeted for, but they massively overspent.

"And now, the Government's refusing to rule out increasing the personal income tax of everyday Australians."

The Coalition has promised to scrap the mining and carbon taxes, and deliver a personal income tax cut.

Assistant Treasurer David Bradbury says those policies would actually put more pressure on family budgets, because the Coalition would cut the associated financial assistance.

Assistant Treasurer David Bradbury says the Government has already delivered $47 billion worth of tax cuts, and he argues the Coalition's policies would actually put more pressure on family budgets.

"Joe Hockey's plans - if you unwind the mining tax, you unwind the carbon price - is to unwind the tripling of the tax free threshold," Mr Bradbury told Sky News.

"He needs to explain what they are going to do in that regard."

Quizzed on the issue this morning, Opposition Leader Tony Abbott reiterated his pledge to fund tax cuts and increased benefits through budget savings, although he has not yet detailed what that will involve.

"I absolutely guarantee to the Australian people, absolutely guarantee to the Australian people that the tax burden will be less under a Coalition government," he said.

Last week, the Government revealed the mining tax raised just $126 million in its first six months.

In the budget, it was forecast to raise $3 billion during 2012-13, although that was later revised down to $2 billion.

The NDIS is estimated to cost $14 billion annually once it is fully rolled out, and Prime Minister Julia Gillard has previous said it will involve "tough choices" when it comes to the budget.