The estimated cost of merging councils into a Wellington super-city has risen by 13 per cent.
The Local Government Commission has released a revised costing for the transition from 9 local councils to one regional body with 21 councillors.
It has now adjusted the cost from $184 million to $210 million.
Commission chair Basil Morrison said external consultants have acknowledged errors in data they provided, concerning estimates for integrating all council IT systems and infrastructure.
Mr Morrison said the revision did not change the commission's preferred option of one super council.