A New Zealand trust company on Wednesday announced it was permanently changing to a four-day working week after a successful trial period earlier this year.

"Productivity went marginally up, stress levels dropped," Andrew Barnes, the chief executive at Perpetual Guardian told New Zealand's AM Show on Wednesday.

The eight-week trial started on March 5 this year and saw the company's entire staff – some 240 people – offered a free day off every week with no changes to their remuneration or working conditions.

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Researchers from Auckland University monitored the trial to observe the impact on the workforce. They found that the reduced hours had no negative influence on staff fulfilling their weekly tasks.

Before the trial, 54 percent of Perpetual Trust employees were happy with their work-life balance, and this increased to 78 percent with the four-day working week in place.

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"What we've seen is a massive increase in engagement and staff satisfaction about the work they do, a massive increase in staff intention to continue to work with the company and we've seen no drop in productivity," Barnes told the New Zealand Herald newspaper.