A New Zealand estate planning firm that made headlines when it trialed a four-day week last year has seen a big productivity increase since it made the change permanent, with staff spending less time surfing the internet.

Perpetual Guardian tried cutting working hours to 30 from 37.5 for its 240 staff in early 2018, asking them to deliver the same amount of output in less time, but keeping pay the same.

The success of the trial prompted it to introduce the policy on a long-term, opt-in basis from last November. Almost four-fifths of staff chose the shorter working week.