New research from NerdWallet, a personal finance site, is making a tough case for active managers to justify their fees.

That’s because the study, which looked at more than 24,000 mutual funds and exchange-traded funds available to U.S. investors for the ten-year period ending on December 31, 2012, found that the asset-weighted average return of the actively managed mutual funds over this period was 6.50% while the passively managed index products averaged 7.30%.

Similarly, for equity funds the average return was 7.19% for active managers and 7.65% for passive funds. Index funds outperformed actively managed funds regardless of whether returns were measured by asset-weighted average, median, or a simple average.

In fact, only 1,863 of the 7,630 of the actively managed products, or 24%, outperformed the index average return of 7.30%. More simply, the majority of people who paid a mutual fund manager to invest their assets over the past decade would have done better by simply investing in a passive index fund, typically at much lower cost, according to the study.

“Active managers earn 0.12% higher annual returns than index investors before fees, but because they charge an average fee of 1.07%, much higher than the average index fee of only 0.15%, active investors are left with 1.10% less than index investors despite their manager earnings superior returns,” according to NerdWallet.