The federal budget could be in the black for the first time in 15 years with Jim Chalmers to forecast a slender surplus of about $4 billion for this financial year.

Despite what would be a dramatic turnaround from a forecast deficit of $37 billion for 2022-23 made just seven months ago, the budget will slip back into the red for the following four-year, forward estimates period, beginning in 2023-24, as spending pressures mount and unemployment grows.