Prime Minister John Key is countering scepticism about the budget's growth forecasts, saying they stack up with other assessments of the economy.

Since the budget was presented last Thursday, opposition parties and some commentators have cast doubt on the reliability of Treasury forecasts and have said it has been wrong in the past.

"Treasury is forecasting 1.8 per cent growth in the year ending March 2012 and 4 per cent growth in the year ending March 2013," Mr Key said at his post-cabinet press conference today.

"That is not aggressive compared with previous recoveries."

Mr Key cited these comments on the Treasury's forecasts:

* ANZ said it thought they were "a bit conservative";

* BNZ said the forecasts were "not significantly different" to its own;

* Deutschebank said the forecasts were "a little weaker" than its own;

* Goldman Sachs said that overall, the forecasts were "broadly similar" to its own; and

* Westpac said that, if anything, Treasury's forecasts seemed "fairly conservative".

"There are many reasons to be optimistic about New Zealand's prospects," Mr Key said.

"We have the highest commodity prices in a generation, our exports are switching strongly towards fast-growing Asia, interest rates are the lowest in 45 years and the Christchurch rebuild will soon be underway.

"I believe we have set a very strong platform for growth and jobs over the next few years."