Treasury has revealed it made a "deeply regrettable mistake" by likely overstating how many children would be lifted out of poverty as a result of the government's Families Package.

Photo: RNZ / Rebekah Parsons-King

The extent of the error - which also affects National's package - is still being determined.

Officials had estimated Labour's plan would lift 88,000 children out of poverty by 2021.

Secretary to the Treasury Gabriel Makhlouf said it is currently remodelling the projected impact of both packages and expects the new numbers to available in late February.

"This is a deeply regrettable mistake and I apologise for it on behalf of the Treasury.

"The Treasury holds itself to high standards and I'm disappointed to have not met those standards here," he said.

The error does not change the number of people affected by the Government's Families Package, the amount of extra income they will receive, or the fiscal impact of the Package.

Treasury said its analysis continues to show the package will "substantially reduce" the number of children in low-income households.

An independent review has also been commissioned to investigate the cause of the error. That review is set to be completed by mid-March.