We examine the daily activity and performance of a large panel of individual investors from Sweden’s Premium Pension System. We find that active investors earn higher returns and risk-adjusted returns than do inactive investors. A performance decomposition analysis reveals that most outperformance by active investors is the result of active investors successfully timing mutual funds and asset classes. While activity is beneficial for some investors, extreme flows out of mutual funds affect funds’ net asset values negatively for all investors. Financial advisors, by contributing to coordinate investments and redemptions, exacerbate these negative effects. Received March 10, 2015; editorial decision September 8, 2016 by Editor Andrew Karolyi

Individuals increasingly buy mutual funds via online platforms, whose “best-buy” recommendations heavily influence flows. As intermediaries of mutual funds, platforms provide none of the unobservable interaction or intangible benefits of brokers, and so allow clean tests of the determinants, influence, and value of their fund recommendations. Using unique U.K. data, we find that platforms favor “own-brand” funds and those paying them a higher commission share. Investors discount own-brand recommendations, but not those paying high commission shares (which were not observable in the United Kingdom). A regulatory ban on commission sharing lowered costs and improved the informativeness of platform recommendations.