New figures confirm what advocates for the poor have been saying for some time - there's a growing gap between rich and poor New Zealanders.

Statistics New Zealand has released data on how the cost of living has impacted the rich and the poor since the National Government took power in 2008.

For superannuitants, inflation has been 19 per cent, for beneficiaries 16 per cent and for big spenders nine per cent.

"The differences are quite big. The lowest expenditure group having double the inflation of the highest expenditure group is quite a marked difference," said Alan Bentley, Statistics NZ senior analyst.

This is making it harder for low income households to pay for things like power and rent.

"We've been seeing for a while now that people at the bottom of the pyramid are actually getting worse off," said James Shaw, Greens co-leader.

But it's pensioners who have been hit worst by inflation.

"Nobody's asking for five star treatment. But some people really do need some assistance because they're in dire straits," said Tom O'Connor, Grey Power president.

But 88 per cent of pensioners own their own home outright, and Prime Minister John Key says their super has also increased.

"Obviously they'll always pick out probably one specific item, but overall New Zealand super is up dramatically over that time and inflation is low," he said.