Updated 7.12pm: Auckland Council is denying reports of a budget blow out, over its mammoth IT transformation project.

After much debate behind closed doors, the council has today revealed the latest figures for its New Core project.

The budget for the merger between the operating systems of the eight legacy councils has grown from $71 million to $155 million.

But council says that's still well within its overall Information Systems budget of 280 million.

The complexity of merging the IT systems of Auckland's eight legacy councils has seen a big hike in the project's budget.

Chief Operating Officer Dean Kimpton says much of the additional funding is required because of how complex the transformation is - something staff only discovered as they began work on it.

He says things are now going ahead full throttle.

"This project is understood in terms of its complexity, it has a plan that we can deliver on, a scope that's understood and a budget to support it."