A KiwiSaver provider wants authorities to take control of an unregulated "wild west" industry that sells "fantasy fiction" to the vulnerable.
Simplicity managing director Sam Stubbs said a survey of six providers, including his own, showed "astounding" differences in the savings estimates between providers.
Using savings calculators on KiwiSaver providers' websites, Mr Stubbs found one provider to have a $900,000 difference to Simplicity's savings estimate, based on the same contributions.
He said it was impossible for savings to vary that much, "unless these managers are the most successful manager in history, anywhere in the world".
"They're lotto numbers, they're fantasy fiction. This is snake oil type stuff."
The calculators of KiwiSaver providers Milford Asset Management, Juno, Generate, Fisher Funds and ASB were asked to calculate the returns for a 20-year-old male, contributing 3 percent from a $40,000 salary, in similar types of funds, through to the age of 65.
The returns varied from around $459,000 to more than $1.3 million.
Mr Stubbs said the estimates varied widely in inflation expectations and often did not include tax deductions.
He said the industry was a "wild west" and calculators were misleading, because they led investors to believe they would get high returns.
The calculators need to be regulated and KiwiSaver providers subject to external auditing, he said.
Milford's head of investments Brian Gaynor said the variances were not surprising, and his provider had high estimates because it made better offshore investments, and in effect it pointed to better returns because it was a better manager.
"In any industry there's wild differences, there always is, because not everybody is the same. We do put a lot of emphasis on the investment side and making the right investments," Mr Gaynor said.
The provider Generate also had projections of more than $1m.
Generate chief executive Henry Tongue said it was difficult to project the future and its figures were clearly marked as illustrative only.
Mr Tongue said he supported industry-wide agreement to reduce large variances.
Mr Stubbs has sent the findings to the Financial Markets Authority (FMA), which confirmed it was looking to see if the calculators might breach rules on fair trading.