Treasury overstated how many children would be lifted out of poverty by the government's families package by 24,000.
Photo: RNZ / Alexander Robertson
The agency publicly apologised in January after revealing it had made an error in its projections.
Officials had originally estimated Labour's plan would lift 88,000 children out of poverty by 2021.
The figure has now been adjusted to 64,000 children.
Deputy Secretary to the Treasury Tim Ng apologised again and reiterated the mistake was "deeply regrettable".
"As we stated in January, the error does not affect the number of people who will be helped by the government's families Package, the amount of extra income they will receive, or the fiscal impact of the package," he said.
"Our analysis continues to show that the families package will substantially reduce the number of children living in low-income households."
The mistake also affected the Treasury's projections for the former National government's family income package announced in May last year.
The agency originally predicted that plan would have lifted 49,000 children out of poverty. The adjusted figure is 33,000.
An independent review into the cause of the mistake is still underway.
Prime Minister Jacinda Ardern said the government's target to reduce the proportion of children in poverty to five percent within a decade remained unchanged, despite the updated projections.
Both the corrected projections and the target relate to a child poverty measure of any household receiving 50 percent or less of the median income before housing costs.