KiwiSaver members have gained about $2.50 for every $1 they have contributed to the scheme, Milford Asset Management data shows.
The scheme is now nine years old.
Individuals have invested $14 billion in their accounts over that time, but have $35 billion between them now.
The $21 billion in gains is made up of $8 billion in employer contributions, $7 billion in government contributions and $6 billion in investment returns.
Murray Harris, head of KiwiSaver at Milford, said: “It’s been a fantastic success for members and the government. How else could have people got $2.50 for every $1 they’ve put away for their retirement.”
But his colleague, Sean Donovan, said more work was needed to help investors get a better result. Too many are still in the wrong type. While 79% of investors over 18 have more than 10 years until they reach retirement, only 30% of KiwiSaver money is in growth and aggressive funds, and 42% is invested in conservative and moderate funds.
“KiwiSaver has been a big success, but this is the one key area that needs to be improved. If KiwiSaver investors don’t begin to take notice of their choice of fund they will end up with a lot less money in retirement than they otherwise could have. It’s too late when you turn 65 to wish you had done better.”