Labor has accused the Morrison government of recklessly riding the coat tails of strong company profits and commodity prices in framing the upcoming federal budget.
Shadow treasurer Chris Bowen said despite billions of dollars in revenue pouring in, Australia's debt levels were rapidly worsening on the Liberal Party's watch.
"Any objective look at the facts shows the Liberals are far from the superior economic and fiscal managers they claim to be," he said on Monday.
"Debt is at record highs, growth has slowed, wages are stagnant, living standards have stalled and demand is lagging."
Deloitte Access Economics expects the government will rake an extra $2.9 billion into its coffers this year than predicted in the last update.
Labor is urging the government to use this windfall to buttress against a potential economic downturn, rather than building tax cuts and other sweeteners into the budget.
The predicted boost comes despite the economy facing local and global headwinds, including falling house prices and deepening trade tensions.
Deloitte is expecting the revenue windfall in the April 2 federal budget because iron ore prices have helped boost company profits and because more Australians have been finding jobs.
Both factors are expected to help the government raise extra tax revenue and flow through to the budget's bottom line, delivering a more modest deficit than predicted this year and a much bigger surplus the next.
Deloitte predicts company profit taxes will hand the government $2.3 billion more than predicted in 2018/19 and $5.2 billion extra in 2019/20.
Taxes on individuals are expected to be $1.2 billion higher this year, and $500 million higher in the next.
Government revenues are predicted to beat official forecasts by $2.9 billion in 2018/19 and $3.7 billion in 2019/20.
That's not a bad result given the flow of bad economic news since the mid-year budget latest was released in December, Deloitte Access Economics Partner Chris Richardson said.
Falling house prices will mostly take bites out of the goods and services tax, which will affect what states receive.
Weak wages growth is expected to be a rising challenge for the budget, meaning it won't have much impact in this year or the next.
"The good news in the economy is concentrated in areas vital to the tax take, whereas the bad news is in areas of secondary concern, thereby allowing the budget to snatch rising revenues from the jaws of a weakening economy," Mr Richardson said.
The economy's strength "where it counts" means the government is also expected to make more savings than expected, by about $400 million in 2018/19.
In its mid-year update, the government predicted a $5.2 billion deficit in 2018/19 and a return to surplus to the tune of $4.1 billion the following year.
Deloitte is tipping a revised deficit of $2.1 billion this year, and a hefty surplus of $9.8 billion the next.
