The Government will boost new spending in this year's Budget, but is hosing down expectations of tax cuts next year.

Finance Minister Bill English said he would bring forward some cash earmarked for 2017, but will not say how much will be injected into the May 26 Budget spending plan.

He had previously earmarked $1 billion for new spending this year and $2.5 billion for the 2017 - election year - Budget with $1.5 billion of that available for tax cuts.

He said lower taxes were still a priority and the Government was committed to cutting personal taxes over time. They would be considered either in 2017 or after, as and when the fiscal situation improved.

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"In particular we want to address the higher marginal tax rates faced by lower and middle income earners as their incomes continue to rise," English said.

But they were dependent on fiscal and economic conditions.

"At this point we've prioritised additional debt repayment over setting aside money in Budget 2017 for tax cuts."

Fiscal conditions "aren't quite there yet" for tax cuts to be possible and the Government had no explicit provision for tax cuts in the forecasts.

But tax cuts were not off the table.

"The right conditions are when we are on top of debt, rather than increasing it, and when the surpluses look sustainable rather than one off."

Speaking at a pre-Budget speech to a Wellington business audience English said "a portion" of the cash available for new spending in 2017 would be brought forward.

Some of that 2017 spending had also been allocated to reduce debt to help meet his 2020 debt target. The capital expenditure allowance would also be lower to help cut debt.

"These changes to the allowance will reduce spending by around $1.2b over the next five years, helping to further reduce debt," English said.

English said the extra spending this year was needed to meet the demand created by population growth, including strong migration.

"When there's more children turning up, you simply have to build the classrooms. There's no choice about that," he said.

"We've also been keen to get debt to actually start dropping. It's still running at about 25 per cent (of gross domestic product)."

Future new spending allowances were likely to be between $1b and $1.5b "and closer to $1.5b", English said.

English reiterated that any move to impose debt to income ratios, to curb house prices, was for the Reserve Bank to decide. His role was to allow the new tool, but the Government would not decide if it was used.

The central bank had indicated it would take "a pretty thoughtful" approach to the use of any new tools.

The tool was unfamiliar here, though it had been used elsewhere. The bank was aware of the trade-offs - that it would make it harder for those borrowing to buy houses - though that was not a reason to shy away from debt to income ratios.