One in 10 New Zealanders live in Australia with the "brain drain" across the ditch no worse than it has ever been, a NZ government study shows.

In fact, the 495,000 Kiwis estimated to be living in Australia represent a smaller proportion of New Zealand's total population than 40 years ago, the Department of Labour study has found.

That's despite 44,000, or one per cent of the country's population, leaving for Australia in the year to June 2011, following a tough year economically and the worst of the Christchurch earthquakes, the report, Permanent and Long Term Migration: The Big Picture, says.

At the end of the 1970s, the departure rate to Australia was equivalent to 1.4 per cent of the then population of around three million, compared with about 4.5 million today.

The report also shows more people have been arriving long term in New Zealand than departing since the 1990s, with the loss of New Zealanders to other lands being made up by migrants from elsewhere.

The report concedes New Zealand has been losing about 4000 more people than it gains in the short term this year, but that this is likely to reverse, particularly as the Australian economy slows.

"Departures to Australia are forecast to ease later this year," said the general manager of the department's Labour and Immigration Research Centre, Vasantha Krishnan.

"We forecast a return to a net migration gain of about 6000 during mid-late 2012 and early 2013."

As to longer term trans-Tasman migration, the report says "New Zealand's population growth provides context to the relative size of migration flows to and from New Zealand but is often overlooked.

"This paper shows that when population size is considered, trans-Tasman departures relative to New Zealand's population are lower now than they were in the 1970s."

About 700,000 to one million New Zealanders live outside the country.