The Green Party has revised its tax policy costings after discovering a calculation error that put the package out by approximately $800 to $826 million, according to RNZ.

The error centred on the treatment of extra funding for Inland Revenue. Rather than being recorded as a cost — as it should have been — it was counted as a revenue measure, inflating the net revenue figures by the same margin. The Greens re-did the costings quietly after identifying the mistake.

The policy itself remains in place. The revised package retains a 2.5 percent annual levy on net assets above $10 million and a 33 percent tax on inheritance or gifts received above $1 million. Those two measures are the main revenue-raising pillars of the Greens' wealth and inheritance tax platform, which has been a defining part of their economic positioning heading into the electoral cycle.

The nature of the error matters as much as its size. Misclassifying an IRD resourcing cost as a revenue line is a fundamental modelling mistake — it overstated net revenue by treating a spending obligation as income. For a party whose core pitch includes the credibility of its fiscal alternative, correcting it quietly rather than proactively is the kind of decision that draws scrutiny in the Press Gallery, regardless of the policy's underlying merits.

The quantum — somewhere between $800 million and $826 million — is not trivial. To put it in fiscal context, that range sits comfortably above the annual operating allowance the current government has been working within. Whether the corrected costings still show the package as a net positive for the Crown accounts is the question the Greens will now face directly.

Wealth taxes and inheritance levies have consistently polled as popular in principle but contested in practice, and the Greens have carried this policy through at least one election cycle already. A costing error of this scale, even when corrected, gives opponents a durable line — and the timing, well outside an election year, may actually give the party more room than it would otherwise have to absorb the reputational hit, recalibrate the numbers, and re-present the policy on firmer ground.