One economist claims the Greens' wealth tax will hit more Kiwis than the Party thinks.

The Greens say  the tax, which has become a hot issue in the final week of the election, would only affect the top six per cent of the population.

However, New Zealand Initiative economist Eric Crampton told Heather du Plessis-Allan the real number's closer to 20 per cent.

He says right now, about 20 per cent of retirees would be subject to it.

And he expects future generations will also build wealth over their lifetime, reaching a peak after retirement.

"We need to be thinking not just about who is currently subject to the wealth tax, but who can we expect to be subject to the wealth tax." 

It comes as Green Party co-leader James Shaw said today the National Party was lying about the Greens wealth tax but at least people were talking about the policy. 

He dismissed suggestions from Jacinda Ardern on Monday that the policy would not even make it to any negotiations table between Labour and the Greens.

"It's not really up to her," said Shaw. "It takes two to tango. We're going to bring it to the table."

But he dismissed the claims from National's Judith Collins that that meant Labour was going to accept it.

"They're obvious lying about it to try and whip up fear but they are also talking about it so that tends to drive people who are interested in fixing the tax system towards us. It is not a bad thing at one level," Shaw told the Herald.