National leader Bill English says Labour may have to "stretch" their money to cover their election promises, and believes they may "fritter away [National's] hard work".
Mr English told the AM Show on Tuesday during National's unsuccessful coalition arrangements with New Zealand First they were "making decisions on the basis of what they would cost", and "would expect [Labour] has done the same".
"There are some big promises in there, I think people would, after the heat of the campaign, want to know what it's going to cost and whether it looks reasonable or not... Because this has all been shrouded in negotiations.
"They've had a few weeks of negotiations with the other parties. And I think people would be reassured if they could put the numbers out now because it's another six weeks or so before the half-year update.
"Either they know and they're not telling it or they don't know which would be not very reassuring."
The Government may have to 'stretch around" their money, Mr English says, and may dig deeper into the country's savings.
"Basically their approach though is to fritter away the hard work that's been done. So [National] built up surpluses, we could've kept going on that, but they're going to spend it up."
Prime Minister Jacinda Ardern defended her Government's "totally affordable" policies after National finance spokesperson Steven Joyce demanded they "front up quickly with the cost of this coalition".
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"Two long-form interviews over this weekend and yet New Zealanders are still none the wiser about the cost of the coalition's programme and the impact on their back pockets," Mr Joyce told The Nation.
But Ms Ardern told the show on Monday the delay is not because the numbers don't add up.
"We want to make sure we've got those numbers right. We've gone and done our own assessment. Now that we're in a position to do so, we're going to make sure we use our access to officials to cost [the policies]. My assessment is it is totally affordable."
Mr English acknowledged how hard it is to get a government organised in the first few weeks.
"They'll be slow, they'll look a bit disorganised, some of the policies will look a bit of a shambles, but that'll all unfold.
"People will measure this on what affect it has on them and what's good for New Zealand, and that's how we're going to measure it."
The full breakdown of the new Government's spending plans will be revealed in the half-yearly fiscal update due before December.