There's one forecast Josh Frydenberg will be pleased the team at the Treasury have got wrong – the iron ore price.

Having pencilled in the price of Australia's largest export to end the June quarter at $US55 a tonne in December's mid-year economic and fiscal outlook, the surge in the active iron ore contract to $US108 a tonne on Monday was rare good news for a Treasurer poised to make history by delivering the biggest budget deficit ever.