The Senate and the deteriorating iron ore price have knocked a $51 billion hole in Treasurer Joe Hockey's first budget, an independent analysis has found. It says part of the problem is that the budget is seen as "unfair".

Presented as Mr Hockey prepares to meet international finance ministers in Brisbane to push for measures to accelerate world growth, it shows the growth outlook for Australia has slipped, with growth of just 2.1 per cent expected in 2015-16 instead of the 3 per cent forecast in the budget.

Budget black hole: Joe Hockey. Credit:Andrew Meares

When the budget was struck in May the iron ore price was $US103 ($119) a tonne. It has since fallen to $US83 taking as much as $10 billion out of tax revenue and helping push wage growth to its lowest level in a decade.

So low has wage growth become that "it seems that not even bracket creep can get the budget back into surplus", says the Canberra consultancy Macroeconomics in a report delivered to clients on Tuesday.