Investor portfolios have lagged market returns by roughly 5% per year over the last two decades.

Mutual fund shareholders will say they are investing for a long time — not timing the market. But the typical fund tells a much different story.

It’s an issue worth exploring now, when both mutual fund flows and the stock market have seen wild swings over the past three months.

Studies show that investors actually don’t capture the full performance of their mutual funds. Boston-based research firm DALBAR Inc. has shown that investor portfolios have lagged market returns by roughly 5% per year over the last two decades.

Meanwhile, academic studies have shown that investors average a return of 2% less than the funds they own, simply because they plow more money into a fund after performance has been hot, and step away or slow deposits when times have been bad.

Investment researcher Morningstar Inc. calculates “investor returns,” tracking how investors do based on when their money flows into a fund. Morningstar research shows that investors earned about 1.5% annually less than their funds over the past decade.