Target-date funds have been on a tear, and it doesn't look like they'll lose popularity anytime soon.
More than $1.1 trillion in assets is now invested in them, according to BrightScope, a researcher that ranks 401(k) plans. That's a 280 percent increase in five years, and BrightScope predicts that $2 trillion will be invested in such funds by 2020.
Target-date funds got a major boost in 2006 with the Pension Protection Act of 2006, which allowed employers to default employees into them if they didn't elect another investment option. Previously, those employees would have been directed toward money market or stable value funds, where those contributors had no chance of growth.