Target date funds surge as more workers put 401(k) plans on autopilot Mutual fund giant Vanguard reported Tuesday that just over half of participants in the 401(k) plans it administers are invested in a single target date fund. These funds — pitched as a sort of Rip van Winkle investment that you can set and forget until you wake up retired — now account for one-third of the assets in all 401(k) and other defined contribution plans run by Vanguard.