Treasury will open up the Government's books on October 6, Treasury Secretary John Whitehead said today.
Finance Minister Michael Cullen has already said it is likely to show a significantly worse fiscal and economic position than in the May budget.
Mr Whitehead said the pre-election fiscal and economic update (Prefu) would indicate the most up to date position an incoming government will face after the November 8 election.
Prefu this time would also include mid-term projections beyond the five-year forecast period and a discussion on the long term outlook.
These would be best on Treasury's best interpretation of current policy, Mr Whitehead said.
Dr Cullen recently said Prefu would paint a bleak picture for 2008, though the economy would begin to recover towards the end of the year.
"It is not going to be a surprise that when the pre-election fiscal update comes out we will all be expecting to see a significantly worse position than was outlined in the budget and any government moving forward has got to be very careful," Dr Cullen said.
The budget predicted ongoing cash deficits of more than $3 billion and this is expected to have worsened.
The Reserve Bank has said that it believed the economy would have recorded negative growth for the first nine months of the year, but it also expected an upturn in activity.
Dr Cullen said the state of the economy meant whoever won the November 8 election their spending options would be limited.
National has again flagged the idea of $50 a week tax cuts, but Dr Cullen was dismissive.
"They are going to find it very hard to argue at all, they won't have to borrow additional funding for any tax cuts."