Fees have become a hot topic in the last year with the entry of new low-cost provider Simplicity.
But the new tool shows having low fees may not be enough to produce the highest net return before tax.
Over the last year to September 30 Simplicity's growth fund had a return of 13 per cent after fees.
Top growth fund Summer KiwiSaver which is run by Forsyth Barr, had a return of 17.3 per cent after fees.
Simplicity had an annual fee of 0.3 per cent compared to Summer's 0.9 per cent.
Likewise paying high fees may not mean savers get the best return.
The highest fee fund in the growth category over one year, the Amanah Growth fund, which had a fee of 2.1 per cent, returned 5.4 per cent after fees.
More than a quarter of its return (27.6 per cent) was eaten up in fees.
The tool also shows that for some funds fees can eat up a large part of the return.
The fee on the NZ Funds Inflation Strategy fund ate up 56 per cent of the return.
The fund had an annual fee of 1.4 per cent and returned 1.1 per cent over the year.
Over five years the Aon Milford Active Growth fund had one of the highest fees but was also one of the best performers.
Its return was 13.8 per cent after a fee of 2.1 per cent was taken off. The fee ate up 13.1 per cent of the return.
Gregory said the tool showed how fees and returns interacted.
"The important thing to understand is that there are two things to this equation."
Gregory said over five years there seemed to be a link between higher risk investments and higher returns.
"However the link between higher fees and higher returns is, apart from in the case of a couple of standout funds, far less obvious."
Gregory said fees and returns were important factors in considering an investment but investors also needed more information before making a decision about where to invest.
The tool also links to Sorted's fund finder tool.
The FMA said the tracker tool used information KiwiSaver providers gave to investors through quarterly fund updates and via the Companies Office's Disclose Register. The tool would be updated three-monthly.
The tool has data for more than 100 different funds and covers five categories - defensive, conservative, balanced, growth and aggressive.