The Conservatives would hold an "emergency budget" within 50 days of winning a general election, David Cameron said.
The Tory leader insisted the financial package would be needed to tackle the soaring public deficit and "get the economy moving again".
Shadow Chancellor George Osborne has already indicated his intention of setting out a Budget early in a new Government.
However, Mr Cameron gave a firmer idea of timing by telling the BBC's Andrew Marr Show it would happen within 50 days of the poll - which must be held by June.
"If we won the election, we would have an emergency budget," he said.
"An emergency budget that, yes, would be about getting the deficit under control and having a credible plan...
"But it should also be a budget that goes for growth, that gets the economy moving again."
Chancellor Alistair Darling said Mr Cameron was being "two faced".
"He says he wants growth but he has opposed our action to help the economy. He has called for cuts now, at the worst possible time since they would choke off the recovery," Mr Darling said.
"As I have said before, we have a choice - a decade of low growth and low employment which is what David Cameron's policies would bring, or securing jobs through higher growth for the future which our policies are designed to do."
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