Of those investors, way too many keep making the same mistakes over and over again -- mistakes that could easily reduce the value of their 401(k) plans.
What's worse, the list of mistakes goes on and on.
"From failing to take advantage of matched contributions to hidden fees that add up, there is more to a 401(k) than saving money," says Nicole Mayer, a financial adviser at RPG Life Transition Specialists.
The worst of the bunch are the ones that can really curb your savings, Mayer says. Here is her list of top mistakes that threaten the financial future of millions of 401(k) savers:
Failing to consider an IRA: "Leaving money in a former employer's 401(k) could add up to thousands of dollars in administrative fees over the long term," Mayer says. "Shifting the savings to an IRA will not only provide a diversified range of investment funds; it is less expensive than those that are actively managed."
Ignoring a matching offer: On the other hand, if a current employer offers to match 401(k) contributions of up to a certain sum, it would be a mistake to not leverage that benefit. "Most employers will match a percentage of your contributions into their employee's accounts," she says.