It is a dangerous game. Politically at least.

Economies and budgets can alter very quickly as a run of uncertain news and events impact on consumers and the business sector. Global shocks come jump out to derail even the best forecasts. Clearly, a lot can change for the budget between now and the Treasurer handing down of the budget on 2 April 2019 Budget.

Even more can change between when the budget is handed down and when the financial year comes to an end on 30 June 2019. This gap alone is a further three months of news that can have a material and unexpected impact on the budget bottom line.

Government spending in 2017-18 will be around $475 billion, a similar number to total revenue. A 1 per cent forecasting error on either revenue or spending could cost the budget close to $5 billion. And 1 per cent forecasting errors have occurred in the past. Mr Morrison’s proud announcement of a surplus seems risky, but it may be a political plus for the beleaguered government. Part of the electorate thinks that the budget balance is a measure of economic management competence and a surplus will be seen, by them, as good news.

But there is a twist.

The final budget outcome for 2018-19 – whether it is in surplus or deficit – will not be known until September 2019, some four months after the voters have made their decision. This means that in the event of a shock Coalition win at the election, the budget could ‘surprisingly’ drop back into deficit but, perhaps ironically, Mr Morrison will still be Prime Minister despite the failure to deliver on his promise.

At the macroeconomic level, there is very little difference between a budget deficit of a billion dollars or two and a surplus of a billion dollars or two. Recall annual GDP in Australia is close to $2 trillion.

But politically, the surplus / deficit issue can be important particularly when the surplus the government says it is delivering cannot be checked until after the election, even though it may sway a few voters to give their vote to the Coalition.