“Taxable investors (those who hold their investments in taxable accounts) owned approximately half of the $11.268 trillion invested in open-end mutual funds, and on average over the last ten years they gave up on an annual basis 0.98 percentage point to 2.08 percentage points in return because of taxes. Taxable equity and fixed income mutual fund shareholders surrendered over 49% and approximately 40%, respectively, of their load adjusted ten-year returns because of taxes.”
Lipper Research, “Taxes in the Mutual Fund Industry–2010: Assessing the Impact of Taxes on Shareholder Returns”