But a further $60 million is needed because "original business case assumptions have not proved correct", as well as an extra $13 million for testing.
The findings of the "reset" phase in the previously confidential report include:
"Technical complexity ... significantly higher than envisaged."
"Disparity of processes across the legacy councils meant significantly more time was spent in discovering these."
"The business case assumed we would be able to use one of the legacy platforms as our base solution ... this proved to not be the case."
"The type of data ... proved significantly more complex than anticipated. This has required increased design, build and deployment effort."
A further $20 million is needed for other planned projects to be brought forward alongside NewCore, bringing the total cost to $171 million - $100 million more than the budget approved two years ago.
But council staff say $25 million of "avoided costs" have been saved by switching technology providers over early.
Chief operating officer Dean Kimpton said there was no change to the overall budget because the extra cost would come out of the $500 million previously budgeted for IT over the next 10 years. But he asked the committee to approve $24 million of capital spending to be brought forward, a recommendation that was narrowly passed after nearly three hours of debate.
While the merits of the project were not questioned by councillors, concerns were raised about the lack of progress reports and oversight since the $71 million was approved in November 2012. Quarterly updates will now be provided and Mr Kimpton said lessons had been learned from other troubled IT projects, such as Novopay.
Several factors had caused the delay to NewCore, said Mr Kimpton.
Chief among these was the technical complexity of amalgamating the systems inherited from the eight previous councils in Auckland - including more than 5000 applications - none of which was suitable as a starting point. The scope of the project had also widened.
Abandoning NewCore, or even slowing progress down, was not an option because the implementation of the Unitary Plan and council bylaws will rely on the success of the technology.
Councillor Cameron Brewer likened the increased cost - which is to come out of the $500 million IT budget - to a house renovation gone wrong.
"It's not about NewCore, it's about the other IT spend. It's like having $100,000 for a house renovation and you want to spend $20,000 on the bathroom - which goes up to $40,000."
Mr Kimpton carried on the analogy: "We're renovating the bathroom and we've found some rotten timber. We've got to fix that, so we'll put the landscaping on hold."
NewCore budget
Original business case: $71 million
Uncovered complexity: $61 million
Testing: $13 million
Other: $7 million
Projects brought forward: $20 million
Total: $171 million
