Mr Hockey, who said the deficit was Australia's second largest in dollar terms, attacked the previous Labor government for the deterioration in the country's debt levels.
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But, speaking in Canberra on Thursday, Mr Hockey and Finance Minister Mathias Cormann said the government had been able to "stabilise" the situation and believed challenges facing the global economy could be beaten.
The opposition rejected the Treasurer's remarks on Thursday, saying the Coalition was to blame for a large portion of the deficit after it transferred almost $9 billion to the Reserve Bank late last year.
Mr Hockey said that 60 per cent of the $30 billion deterioration in the bottom line was from the write-down of receipts, particularly tax receipts.
"This comes down to the fact that Labor continually overestimated the amount of tax that they would collect, they continually got it wrong," Mr Hockey said.
"This is not a confected figure. It is the real numbers."
Mr Hockey said that government decisions, including his call to transfer $8.8 billion to the Reserve Bank, accounted for $11 billion of the $30 billion blowout.
"That is money that would come out of the budget at some point, because the Reserve Bank reserve fund needed to be replenished, either at that point of time or in the future," Mr Hockey said.
But he added that there were "a number of miscalculations by the previous government", including of the revenue from the now-repealed mining tax, which was expected to raise around $700 million but only raised $100 million.
The Treasurer said there had been an "overly optimistic" approach to economic forecasting and called for "a more realistic approach to forecasts".
"Wayne Swan promised this year would be a surplus. It's a $48.5 billion deficit," Mr Hockey said.
"That is a dramatic change in two years."
He said the government would release the mid-year economic and fiscal outlook in December.
Mr Hockey, who hailed a weekend meeting of G20 finance ministers as a success, said countries such as Germany and China were taking "fiscally prudent" steps to address challenges in their economies.
"There are significant global challenges, but they can be beaten. They can be beaten," he said.
Coalition government's responsibility
Shadow treasurer Chris Bowen and opposition finance spokesman Tony Burke hit back at the Treasurer's claims.
They said the Abbott government was responsible for the decline, having been in control of the budget since September last year.
"Last time we checked, the Abbott government has been responsible for budget and economic policy since September 2013. That's 75 per cent of the 2013-14 financial year," they said.
Labor said that under the Abbott government the deficit had deteriorated from $30.1 billion in the pre-election economic and fiscal outlook to $48.5 billion.
"Of the $18.4 billion blow-out, over half - $10.8 billion – is due to policy decisions taken by the Abbott government, including the $8.8 billion grant to the Reserve Bank of Australia," Mr Bowen and Mr Burke said.
