Average fees also tend to vary based on the size of an employer's 401(k) plan. The total management costs for individual companies with plans with more than $1 billion in assets has averaged 0.35 percent a year, according to BrightScope, a firm that rates retirement plans. By contrast, corporate plans with less than $50 million in assets have total fees approaching 1 percent.
Higher management costs do far more to erode a typical American's long-term savings than does the high-speed trading highlighted in Michael Lewis' new book, "Flash Boys." Kinnel said computerized trades operating in milliseconds might cost a mutual fund 0.01 percent during the course of a year, a microscopic difference compared with yearly fees.
"Any effort to shine more light (on fees) and illustrating that impact is huge," Kinnel said. "Where we've fallen down most is not providing greater guidance for investors in selecting funds."
The Investment Company Institute, a trade group, said 401(k) fees for stock funds averaged 0.63 percent in 2012 (lower than the 1 percent average figure the Center for American Progress uses), down from 0.83 percent a decade earlier. The costs fell as more investors shifted into lower-cost index funds. They've also declined because funds that manage increasing sums of money have benefited from economies of scale.
"Information that helps people make decisions is useful," said Sean Collins, the institute's senior director of industry and financial analysis. "Generally, people pay attention to cost. That shows up as investors tend to choose — including in 401k funds — investments that are in lower than average cost funds."
But many savers ignore fees.
In a 2009 experiment, researchers at Yale and Harvard found that even well-educated savers "overwhelmingly fail to minimize fees. Instead, they placed heavy weight on irrelevant attributes such as funds' (historical) annualized returns."
The Labor Department announced plans last month to update a 2012 rule for companies to disclose the fees charged to their 401(k) plans. Fee disclosures resulting from the 2012 rule proved tedious and confusing, said Phyllis Borzi, assistant secretary for the Labor Department's Employee Benefits Security Administration.
"Some are filled with legalese, some have information that's split between multiple documents," Borzi said.
Americans hold $4.2 trillion in 401(k) plans, according to the Investment Company Institute. An additional $6.5 trillion is in Individual Retirement Accounts.
For years, companies have been dropping traditional pension plans, which paid a guaranteed income for life. Instead, most offer 401(k)-style plans, which require workers to choose specific funds and decide how much to contribute from their pay. Workers also bear the risk that their investments will earn too little to provide a comfortable retirement.
The shift from traditional pensions threatens the retirement security of millions of Americans. Many don't contribute enough or at all. Some drain their accounts by taking out loans and hardship withdrawals to meet costs. Sometimes their investments sour. And many pay far higher fees than they need to.
Of all those problems, fixing the fees is the easiest, Center for American Progress researchers Jennifer Erickson and David Madland say.
They are calling for a prominent label to identify how a plan's fees compare with low-cost options. That information, now found deep inside documents, shows the annual fees on investing $1,000 in a plan. Yet that figure, usually only a few dollars, doesn't reflect how the fees rise into tens of thousands of dollars as the account grows over decades. The researchers say the Labor Department could require more explicit disclosure without going through Congress.
Part of the blame goes to employers that offer workers high-fee plans.
"The good options are out there," said Alicia Munnell, director of the Boston College's Center for Retirement Research. "But when you introduce bad options into a plan, you attract people to them. There are a lot of people who think they should buy a little of everything, and that's diversification.
"I want the world to know that fees can really eat into your retirement savings."