Power Play - The government will open the books today, which will give political parties an idea of what extra money they may have as they finalise election campaign promises.
Photo: Flickr -William Warby - (CC BY 2.0)
That could be as high as an extra $1 billion a year.
The latest financial statements (PDF, 2.1MB) show the surplus was $1.5bn ahead of expectations, due to surging tax revenue and tight control over spending.
But if parties want to announce policies that require year-on-year funding, they will be looking to see whether any extra money is a one-off or can be counted on for a number of years.
All signs point to an economy that has some momentum, underpinned by strong migration, low interest rates and record tourism.
National Party leader Bill English said it was up to Treasury to reveal the Pre-Election Fiscal Update (PREFU), but he appeared confident it would paint a rosy picture.
"The economy's on a good track, the government's books are sound, we've got positive choices and we're making them."
The update would reflect National's "sound financial management", he said.
"Because we've got surpluses, if you keep managing the expenditure sensibly, we don't need to increase taxes which is why Labour is starting to struggle - not only the detail of those taxes but why we need them."
Mr English criticised Labour's spending plan as "high level and unfocused".
"If you're spending taxpayers' money you've got to show you can get results - they can't show that."
Labour's leader Jacinda Ardern said until the PREFU the party would not have a clear sense of how much money would be available for a future government.
She said that once Labour had a chance to look at the books, she would be telling the voting public what changes a Labour government would make to personal income tax rates.
In the 2014 election, then-Labour leader David Cunliffe campaigned on raising the top tax rate to 36 percent on incomes above $150,000, a policy dumped by his successor Andrew Little.
Ms Ardern also said she retained the right for a Labour government to introduce a capital gains tax.
When asked to rule out a capital gains tax on farms or business, Ms Ardern said the only commitment she was willing to give at this stage was that any capital gains tax would exclude the family home.
"Beyond that, I am leaving it to a group of experts to work through what we need to do more broadly when it comes to our taxation in New Zealand."
Labour has already unveiled its alternative budget but a significant tertiary policy aimed at easing the cost of living for students, and potential further investment in health, education and housing could be on the cards.
National has already responded to pressures, particularly in the health sector with announcements about rebuilding Dunedin Hospital and better access to GPs for lower income families in the past week.
In the May Budget it also unveiled a major families package containing a boost to Working for Families, the accommodation supplement, and tax cuts.
The party also signalled it would like to extend the tax cuts further if it had the financial room to do so.