If Treasurer Scott Morrison still considers a company tax cut as part of his first budget, a former Reserve Bank governor believes it will do more harm than good.

With less than three weeks to go, the likely content of the May 3 federal budget remains unusually vague, other than it will include the results of the government's tax review.

A GST increase and personal income tax cuts are off the agenda, although the government has talked up the benefits of cutting the 30 per cent company tax rate.

But former central bank boss Bernie Fraser disputes claims businesses would invest more and the economy would grow if there was tax relief.