The Greens say they can meet all their policy promises and still run budget surpluses.
They've put all their election policies together in a single document and it's been checked out by Infometrics, an independent economic consultant.
"Infometrics has found that the Green Party will run surpluses over the next three years, slightly smaller than those outlined in the Pre-election Economic and Fiscal Update (PREFU)," the party's fiscal plan, released on Monday, says.
PREFU forecast surpluses of $2.9 billion, $3.5b and 5.7b for the next three years.
The fiscal plan says the Greens will be able to take "significant steps" in the first parliamentary term to address child poverty, make lakes and rivers swimmable and tackle climate change.
"We can meet these challenges while being fiscally responsible by raising some new revenues," the document says.
"For example, through a new, comprehensive capital gains tax - excluding the family home - and by finding savings from low-value government spending."
That's where the plan runs into a problem, because the only way the Greens can get into Government is by going into coalition with Labour which has ruled out any new taxes in its first term.
The fiscal plan sets out in detail, and confirms, all the Greens' previously announced policies.
It sets the 2050 goal for a carbon-neutral economy - the same as Labour's - and 100 percent renewable energy by 2030.
It would invest $11 billion in clean, safe, rapid transport over the next decade, put $100 million into Kiwibank to help it expand into commercial banking and give tax breaks for electric vehicles.
It would put a levy on nitrate pollution from agriculture, double the number of conservation rangers, and put a charge of 10 cents a litre on exported bottled water.
The bottom tax rate would be reduced from 10.5 percent to 9 percent on income under $14,000, and there would be a new top tax rate of 40 percent on income over $150,000 a year.
Health and education funding would be returned to "real levels" at the same rate Labour is promising.