The federal budget also faces a huge spike in spending if crucial NDIS reforms are delayed past October, which will dwarf the recent tax U-turns.

The federal budget also faces a huge spike in spending if crucial NDIS reforms are delayed past October, which will dwarf the recent tax U-turns.

Billions in budget savings hang in the balance as the government prepares for a high-stakes showdown over the future of the NDIS.

Treasurer Jim Chalmers is clocking it up as a major victory, but his tax package has received a mixed scorecard from the experts.