Questions are being raised over whether the Green Party's proposed tax overhaul is needed.

It's pledging to lift the top tax rate to 45%, corporate taxes to 33%, and slash taxes for earners below $120,000.

Assets worth two-million-dollars will be hit with a 2.5% wealth tax — or four-million-dollars for couples.

Trusts will also be taxed at 1.5%.

But, New Zealand Initiative Chief Economist, Eric Crampton says that a new tax system isn't the way unless you want the Government to raise substantially more money.

He says if you want something like an Income Guarantee programme, far more tax will need to be raised.

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