The Treasury and Statistics New Zealand have miscalculated figures on household income, leading them to overestimate the disposable incomes of low- and middle-income households.
In a statement, the two government departments say the estimates from 2007 to 2012 are incorrect.
They say their revision of the figures shows the number of children estimated to be living in households earning 60 percent or less of the median income has risen from 265,000 to 285,000.
However, the Treasury's chief economist, Girol Karacaoglu, says the department's advice to the Government would not have changed if it had had the correct figures.
