Economists say Labor has a realistic chance of posting a shock third budget surplus as soaring tax revenue delivers Treasurer Jim Chalmers a $14.5 billion windfall that could allow the government to promote its economic credentials or spend more cash during the election campaign.

Booming income tax from a strong jobs market and a weak Australian dollar that is turbocharging company taxes on US dollar-priced commodity exports have helped slash the budget deficit in half. The deficit in the five months to November 30 was $14 billion, versus an expected deficit of $28.5 billion to that point in the year, according to Department of Finance figures.