There is just one figure you need to know about Swan Are we ignoring the elephant that's just died in the room? Only six months ago Prime Minister Julia Gillard was still sure she would end this financial year with a surplus: We stand by the predictions, the entries in the Mid-Year Economic and Fiscal Outlook. We stand by the figures and we're on track to deliver a budget surplus. Remember, that was just six months ago. Yet now the Treasurer admits the deficit this financial year is actually $19.4 billion. Somehow, in the space of six months, the Government ended up $20 billion behind what it had thought and what it had promised. That is an astonishing amount of money. To put it in scale, it is the more than the full costs of the government's proposed disability scheme and its Gonski changes combined. How on earth could you make such an astonishing bungle over so short a period, especially with no sudden changes in the world or domestic economy? That is incredible enough. And utterly damning. But here's another curious fact about that figure. Three weeks ago Gillard said she was receiving $12 billion less in tax revenue than what she'd expected when she got the MYEFO figures back in October: So three weeks ago Gillard told us she was down $12 billion on what she expected in October, two weeks before she again promised she'd still deliver the surplus. Yet the deficit announced yesterday is not $12 billion but $19.4 billion. How did another $7.4 billion go walkies in just three weeks? The story of this Budget - and the Government's financial credibility - should begin and end with this single figure: the $19.4 billion deficit that has come from nowhere.