Australia's first budget surplus in more than a decade is built on "very realistic, very cautious" assumptions about future growth, with more surpluses to come.
Finance Minister Mathias Cormann says the coalition has taken a conservative approach to forecasts on commodities like iron ore in Tuesday's federal budget.
"Our forecasting assumptions are very realistic, very cautious, very responsible," Senator Cormann told Sky News on Sunday.
'In the first few years of coming into government we had to write down revenue by more than $180 billon compared to the revenue forecasts that we inherited."
Senator Cormann said looking at the 2016/17 and 2017/18 final budget outcomes, the coalition outdid its own predictions.
"Our actual performance against budget was materially better than what was forecast at budget time and principally on the back of stronger economic growth, stronger employment growth," he said.
"From 2019/20 onwards our forecast and projections are for a surplus to be maintained all the way through the medium term over the next decade."
But despite the 2018/19 budget deficit being reduced to $5.2 billion in the mid-year economic and fiscal outlook statement, Senator Cormann refused to say if it will also end up in surplus.
Shadow treasurer Chris Bowen said the coalition had over-estimated wage growth in every single budget it had handed down.
"The treasurer changes from budget to budget, it seems. But the fact that they don't meet their wages forecast doesn't change," Mr Bowen told ABC's Insiders.
Labor is planning to do its own budget within months of winning the federal election if the party takes power in May.
