The Minister Responsible for Novopay says the cost of fixing the flawed school payroll system will reach $43 million by the middle of this year.
Steven Joyce said on Thursday that the additional costs of remediating Novopay hit $33 million at the end of last year and the Ministry of Education expects to spend a further $10 million by June.
Mr Joyce said it is not clear how much of that Novopay designers Talent2 from Australia will pay.
"Right at the outset, we said that the discussions around who would be responsible for what elements the remediation would take some time, because there's fault on both sides - we know that.
"That was made clear in the ministerial review, so there will be discussion and some quite robust discussions about who is responsible for which parts."
More than than 660 school staff at 432 schools were incorrectly paid in last week's school pay-day. Mr Joyce said the error rate is still too high, but the problems are with data entry and the service centre that deals with school's problems, rather than with the Novopay software.
The minister said the Government is not considering replacing Novopay.
