The amount of money invested in KiwiSaver grew by nearly $10 billion last year as local and global share markets continued to perform strongly.
Figures from research firm Morningstar show the amount of money invested in KiwiSaver rose from $35.7 billion at the end of 2016 to $45.6 billion in December 2017.
That compares to the growth in 2016 which saw assets rise around $6b and 2015 where they grew around $5b.
Chris Douglas, director of manager research ratings, Asia-Pacific for Morningstar Australasia, said 2017 had been a "great year" for those investing in shares with the local market posting 22 per cent growth and the MSCI World Index up 20 per cent.
"Pleasingly, all KiwiSaver funds managed to produce positive returns in the year across the multi-sector categories."
Douglas said during 2017 funds in the aggressive growth category grew on average by 13.56 per cent while those in the conservative category rose on average 3.63 per cent.
The highest performing fund was the OneAnswer International Share fund which rose 24.2 per cent in 2017.
Although Douglas said it was "most appropriate" to consider the performance of a fund over the longer term.
Over 10 years the top performing fund has been Milford's Active Growth fund which has had an average annual return of 12.8 per cent.
The average performance for conservative funds over the last 10 years was 5.9 per cent. For the balanced category it was 6.4 per cent and for growth 7.3 per cent.
The largest provider remains the ANZ which manages $11.6 billion, followed by ASB with $8.4b and Westpac with $5.5b.
Morningstar said the six largest providers accounted for 83 per cent of the assets on its database.
More than 2.7 million people are signed up to KiwiSaver.