Trust chief executive Darren Burden said last night the increase was a result of cash flow problems caused by a trend towards annual, rather than upfront, payments for corporate suites and membership packages the trust is selling.
That meant the trust would have to pay for bridging finance to cover the shortfall.
Mr Burden said the trust was confident it could meet the new target.
The increase emerged when Mr Burden was asked about a report to this Monday's Dunedin City Council finance and strategy committee meeting, which gives an update on the trust's work.
The report also reveals the trust has received a written offer for head naming rights of the stadium.
However the offer, which remains valid for six months, does not meet the trust's expectations and it "may continue to market this sponsorship product".
The trust had set itself a task of raising $45.5 million in private funding to help pay for the stadium.
The council heard last month only 53% of private sector funding was forecast to be received before the stadium was built.
The report said written expressions of interest in corporate box and membership packages equated to a capital funding contribution of $14.2 million.
Funding raised by the trust has to go towards both capital funding, for building the stadium, and operational revenue.
Mr Burden said when the trust originally considered gathering money from seating packages, it expected to receive money upfront, as had been the experience of the Westpac Trust Stadium, in Wellington.
"The Westpac Trust Stadium sold theirs for a 15-year period, but sold them for a lump sum upfront," he said.
The market had changed. People would much prefer to have a 10-year commitment, but pay annually.
The trust was "very comfortable" with its chase for private funding.
"We've got 25% . . . already."
Asked if the increase was the sort of blow-out in cost about which some people had raised concerns, Mr Burden said the target had changed, but so had the design of the stadium.
The seating packages available, which were confirmed by the design of the stadium, would raise the $45.5 million.
If only one-third of "high end" products, like the Founders Club and the Roaring 40s club packages, were sold, the extra $10 million would be covered.
Dunedin deputy mayor Syd Brown said the increase came from the council's requirements for the trust.
The trust had planned to borrow to deal with cash-flow problems, but the council had said no, which meant the trust had to find the extra money.
Asked if he thought raising the extra money was possible, Mr Brown said that was a task for the trust.
