George Osborne has played down suggestions he will be forced to find more spending cuts or put up taxes in order to balance the books by the time of the next general election.
The Chancellor was forced to announce more than £50 billion of additional borrowing in the Budget on Wednesday after the Office for Budget Responsibility (OBR) sharply downgraded its outlook for the economy.
However, he insisted he would still be able to meet his self-imposed target of delivering a budget surplus by the time of the election in 2020.
"We have got to hold to the course that we have set out," he told BBC1's Breakfast programme.
"I have set out the plans in the Budget and then a completely independent body which everybody respects - the Office for Budget Responsibility - has looked at those plans and it says, 'If you hold to the course, you deliver those plans. If the economy grows as expected, then we will have a surplus towards the end of the parliament'.
"We wouldn't need anything extra like more spending cuts or more tax increases."
However, Institute for Fiscal Studies director Paul Johnson said Mr Osborne had only been able to make the figures add up by "shuffling money around".
He warned that the Chancellor would be forced to find "genuinely big" tax rises or spending cuts if there was any further downgrade in the public finances.
"Within his very tight rule he will probably get away with this this time round. But there's only about a 50-50 shot that he's going to get there," he told BBC Radio 4's Today programme.
"If things change again, if the OBR downgrades its forecasts again, I don't think he will be able to get away with anything like this. I think he will be forced to put some proper tax increases in or possibly find some yet further proper spending cuts.
"I think this is going to be the last chance he gets to move things around like this without doing anything genuinely big to the public finances."