The latest study into Kiwisaver shows the money now invested is less than the amount so far paid in by members and the Crown.
Kiwisaver, which is intended to help boost superannuation saving, had its second anniversary earlier this year.
The report by Inland Revenue and two other agencies says 1.1 million people had signed up by the end of June.
In the year to June, an average of 32,000 people a month joined the scheme.
The scheme is managing $3.039bn of assets, which is $115m less than the total of $3.154bn invested by the public and the Crown in the two years.
Revenue Minister Peter Dunne says that difference is due to fund performance and fees.
The report says 78% of the money is invested with nine providers out of the 30 available.
Numbers signing up have slowed since the first year and it's forecast membership will eventually plateau at about 1.4 million.
The snapshot also reveals 180,000 children are signed up although its believed most are not adding to the $1000 kickstart provided by the Government.