The surplus is nearly $1b less than forecast at last month's budget, says Finance Minister Bill English.

The Government's surplus is nearly $1 billion less than forecast at the budget.

The Government's financial statements, released on Friday, showed the operating balance before gains and losses (Obegal) was $297 million in the black for the 10 months to April.

Finance Minister Bill English said it highlighted the monthly volatility in the Crown accounts.



The surplus was $941m smaller than forecast in Budget 2016, largely as a result of core Crown tax revenue coming in $1.1 billion lower than forecast.



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"Tax revenue can fluctuate significantly from month to month," English said.



"What is important is the overall trend, which shows the Government growing surpluses and getting on top of debt."



At last month's budget, Treasury delivered a growth forecast of just under 3 per cent a year, for the forecast period, and unemployment would hover around 5 per cent.



That was expected to deliver surpluses in the order of $719m next year to $2.46b in 2018, $5b in 2019 and $6.7b in 2020.

English said the lower-than-expected tax revenue was mostly driven by corporate tax being $1.4 billion below forecast.

"Treasury consider that most - if not all - of this variance will reverse out by June 30."

Core Crown expenses were in line with Treasury's Budget forecasts, and remained on track to stay below 30 per cent of GDP in 2015/16 – down from 34 per cent in 2008/09, he said.

"The Government measures success by the results we achieve for New Zealanders, not by spending more in an attempt to show that we care."