Treasurer Scott Morrison isn't disputing a new report predicting a $24 billion deterioration in the budget over the next four years but neither will he confirm whether a surplus is still on the cards in 2020/21.
Instead he stated the obvious - Australia's finances will be back in the black when expenditure is less than revenue.
"You don't have to be a rocket scientist to work that out," Mr Morrison said in response to a Labor question during parliamentary question time on Monday.
Deloitte Access Economics predicts a boost to national income from a sharp rise in coal prices will only partly offset a deterioration in tax revenues on the back of record low wage growth and job creation undershooting official forecasts.
Its economist and ardent budget watcher Chris Richardson expects the budget deficit to be $40.5 billion in 2016/17 rather than the $37.1 billion forecast in the May budget.
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"Wage growth will lift more slowly than Treasury had pencilled in to the budget figures, that says ongoing write-downs to budget repair," Mr Richardson said on Monday.
Figures last week showed annual wage growth has dropped to just 1.9 per cent, the slowest in at least two decades.
In the May budget, wage growth was forecast at 2.5 per cent in 2016/17, rising to 3.5 per cent in 2019/20.
The treasurer said while Mr Richardson's work was very thorough, he obviously didn't have access to the data that's still to come, such as the September quarter national accounts.
Mr Morrison will hand down the mid-year budget review on December 19.
But opposition finance spokesman Jim Chalmers is concerned the country's triple-A rating is now at an even greater risk of being lost, saying the government must abandon its planned business tax cuts.
It was a "$50 billion ram raid" on the budget.
"Australia can have a AAA credit rating or it can have a $50 billion gift to big multinational corporations, but it can't have both," Mr Chalmers told reporters in Canberra.
Former Liberal leader John Hewson agreed the risk of the government losing the top tier rating was "very real".
"I don't think they are going to save it. They have allowed this situation to drift," the professor of economics told Sky News.
Mr Morrison said about $19 billion in savings were being blocked by Labor in the parliament.
"If they are so concerned like they say about the fiscal position of the budget, pass the savings," he said.
Instead, the treasurer said every time Labor sees an estimate which shows some pressures on revenues, it thinks all you need to do is "keep squeezing the tax lemon" as hard as it possibly can.
DELOITTE ACCESS ECONOMICS BUDGET FORECASTS
(deficit forecasts vs May budget predictions)
2016/17 - $40.5 billion vs $37.1 billion
2017/18 - $29.9 billion vs $26.1 billion
2018/19 - $22.5 billion vs $15.4 billion
2019/20 - $15.9 billion vs $6.0 billion
