A drop in spending has netted the federal government a $15.8 billion surplus for the most recent financial year, despite the government's tax take also falling in that time.

The final budget outcome is $6.4 billion better than the $9.3 billion surplus forecast in May.

That improvement has come almost entirely from lower spending, according to the federal government, with payments as a share of total economic activity about 2 percentage points below what was forecast two years ago.

And it comes despite a drop in revenue over that time.

It means the federal government has delivered two back-to-back surpluses, driven during that time by strong commodity prices and a larger income tax take from more people being in work.

Lingering high inflation for the past two financial years forced the government to pocket most of the savings and revenue upgrades it made, with spending largely limited to targeted relief to cost-of-living pressures to avoid further fuelling inflation.

However, internal analysis prepared for the Reserve Bank in June determined the government's budget for this financial year was expected to be "slightly expansionary", despite inflation still sitting above the RBA's target of 2 to 3 per cent.

Underlying inflation, which the Reserve Bank is now following closely to determine whether to adjust interest rates, was at 3.4 per cent over the year to August.

The government says 87 per cent of revenue improvements were returned to the budget.

Treasurer Jim Chalmers said the double surplus was the first in nearly two decades.

"Our bigger-than-expected surplus in the year just gone is entirely due to lower spending, with the tax take also lower," Mr Chalmers said.

"This kind of responsible economic management would be unrecognisable to our predecessors."

Finance Minister Katy Gallagher said disciplined spending had allowed the government to invest more elsewhere.

"Posting back-to-back surpluses is a key part of our plan to take pressure off inflation while providing relief to families, who we know are under pressure," Senator Gallagher said.

Overall, the budget position has improved by a cumulative $172.3 billion compared to the pre-election forecast.

The release of the final budget outcome for 2023-2024 will also reveal Australia's net debt, which sat at $517 billion when Labor took office in May 2022.