Employees who were enrolled automatically in "default" KiwiSaver schemes lost almost half of the money earned on their savings in the past year - through providers' fees.
The Financial Markets Authority's annual report on KiwiSaver, issued this month, shows the six default providers charged a total of $43 million in fees on fund earnings of only $104 million - a fee ratio of 42 per cent.
Non-default providers charged $121 million in fees, or 28 per cent, on fund earnings of $432 million.
A non-default fund provider who analysed the report, Michael Chamberlain, said the default providers' high fees highlighted risks in a Government plan announced on Tuesday to enrol all remaining employees in default funds in 2014-15, although they have a right to opt out again if they choose.
"If the Government is going to auto-enrol all other employees, surely it would want to auto-enrol them into schemes where the fees are reasonable," he said.