Corp tax plan ambitious enough: Treasurer

Cutting the corporate tax rate to 25 per cent will thrust Australia into "the middle of the pack" compared with global markets, Treasurer Scott Morrison says.

Asked if slashing the tax rate would make any real impact if those in other markets keep tumbling, Mr Morrison said the 10-year target would "put the country back in a far more competitive position".

"It puts us in the middle of the pack over that period on OECD averages currently," he told reporters at a Tax Institute breakfast in Sydney.

Mr Morrison also sought to quash claims his 10-year corporate tax plan wasn't costed in Tuesday's budget.

"If you look at the medium-term projections on the underlying cash balance, it goes out to (2026/2027), and our full tax plan is incorporated in those projections as provided for by Treasury," he said.

"So it's fully accounted for, it's there."