Treasurer Scott Morrison has nominated finding money for disability services and defence as key priorities for his first budget.
Mr Morrison will deliver the budget on May 3, possibly ahead of a double-dissolution election on July 2.
The treasurer said he was focusing on getting government payments as a share of GDP down, while finding billions of dollars for the national disability insurance scheme and defence projects.
Government payments as a share of GDP are forecast to decline from 25.9 per cent in 2015/16 to 25.3 per cent in 2018-19.
But disabilities spending is expected to grow by 67 per cent in real terms over the next four years, as the NDIS is rolled out at a cost of $37 billion.
The Defence white paper also commits the government to lifting spending on the military to two per cent of GDP, with $32.8 billion set aside this year.
“(We have) significant pressures on the budget,” Mr Morrison told ABC radio on Friday.
“Projects like the NDIS, ensuring our defence forces get the support they need … you have to have the discipline to ensure that you keep your expenditure under control going forward.”
Mr Morrison rejected suggestions there was a problem with money coming in, saying revenue as a share of the economy would be higher than the long-run average next financial year.
He would not return to the “old economy way of tax and spend”.
Media reports suggest the budget will keep in place work-related tax deductions and a company tax cut announcement will outline a “trajectory” rather than a specific percentage cut in 2016/17.
There are also reports the government will tackle high-end superannuation tax breaks.
“The tax mix, I think, is a very valid issue and the government continues to pursue those issues,” Mr Morrison said.
Opposition Leader Bill Shorten told a forum in Brisbane on Thursday night a Labor government would “start fixing up the budget”.
“We are committed to budget repair that is fair,” he said, pointing to a greater tax return from multinational corporations and wealthy superannuants.