Finance Minister Bill English has set May 21 as the date for National's seventh Budget.

"Our ongoing commitment to spending restraint means the public finances continue to improve significantly each year," English said in a statement. "Since we were first elected in 2008, we have seen the economy move from a recession to sustained growth, and New Zealanders are now being assisted by low unemployment, stable low interest rates and wages that are growing faster than inflation."

In December, the Treasury pushed out the government's forecast return to operating surplus until 2016, as persistently low interest rates erode revenue from withholding taxes, household spending lagging estimates saps the goods and services tax take, and soft inflation keeps a lid on wages, crimping income taxes. The Treasury forecast an operating balance before gains and losses (Obegal) deficit of $572 million in the year ending June 30, 2015, turning to a surplus of $565 million the following year.

The Obegal deficit "has shrunk significantly from a peak of 9 per cent of GDP in 2010/11,"English said today. "We will know in October, when the final Crown accounts are published, whether a surplus was achieved 2014/15."

"The global economic environment remains uncertain, and this makes it even more important to maintain responsible fiscal management," he said.