"One example of a service market where there may be scope for similar intervention is the KiwiSaver funds management," the commission said.
Commission for Financial Literacy and Retirement Income spokesman David Kneebone said KiwiSaver was not among most people's priorities.
His team had met the Productivity Commission this week to discuss that report and the tool being developed. "This will satisfy some of that need."
Investors should not look at historic returns as a gauge for the future and fees were a significant part of any decision, he said.
About a quarter of all KiwiSaver members are still in the default schemes they were automatically enrolled in. These are invested conservatively, which usually suits older investors best, and returns are usually lower over a long time. Default schemes returned between 5.3 per cent and 6.8 per cent in the year ended June, compared with up to 26 per cent for aggressive funds.
Milton Jennings, CEO of Fidelity Life, which sold its KiwiSaver business to Grosvenor, said any tools that helped people understand their investments were useful. "Now balances are starting to grow, people are taking more of an interest."
He said it was important to understand that high-risk investments, such as equities, involved periods of correction as well strong growth.