Prime Minister Tony Abbott has set his sights on the budget's small business package clearing parliament's lower house this week.
But its childcare measures are likely to face a tougher challenge because they are tied to controversial family tax benefit changes from last year's budget that are being stymied by the Senate.
MPs returned to Canberra on Monday for a two-week sitting of the House of Representatives as senators drill down into the budget numbers during estimates hearings.
The release of Labor-commissioned modelling of the budget to selected media coincided with parliament's return.
The National Centre for Social and Economic Modelling analysis reveals the poorest families will lose about seven per cent of their disposable income over the next four years because of the budget.
Opposition social services spokeswoman Jenny Macklin said the only way to protect families was for the Senate to reject changes to family tax benefits.
Social Services Minister Scott Morrison dismissed the report, saying it ignored the measures the government had put in place to help people into work rather than onto welfare.
"What (Opposition Leader) Bill Shorten is saying is, he wants a bus from the school to get to Centrelink from the moment someone leaves school," Mr Morrison told Sydney's 2GB radio.
Mr Abbott challenged Labor during question time to release the full analysis.
"If this modelling is to be taken seriously, it must be released ... every moment that the modelling is kept hidden by members opposite demonstrates that even they fear that it can't all be taken seriously," he said.
Treasurer Joe Hockey lampooned the report, telling parliament he had unearthed the Natsem modelling that he said amounted to "two whole pages" from Mr Shorten's office.
Still, the business package, which will give small firms tax cuts and a $20,000 instant asset write-off, looks set for a relatively smooth passage.
The Westpac-Melbourne Institute small business index suggests it cannot come quick enough, showing confidence fell to its lowest level in over a year before the release of the budget.
Mr Abbott is confident that jobs growth will accelerate because of the budget's measures.
"This is a budget for confidence ... (Labor) want to talk doom, talk gloom, talk our economy down," he said.
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