The average balance of 401(k) retirement plan accounts managed by Fidelity Investments rose to $74,900 at the end of the first quarter, the highest level since the company began tracking balances in 1998.
That's an increase of 12 percent from a year ago, Fidelity said Wednesday.
By comparison, the Standard & Poor's 500 index climbed 13.4 percent in the 12-months ended March 31.
The account balances increased about 58 percent from the same period in 2009.
About two-thirds of the increase can be attributed to stock market growth and one-third is the result of workers' own added contributions and company matches, said Beth McHugh, Fidelity's vice president of marketing insight.
The balance figures were based on the accounts of about 11 million workers enrolled in plans Fidelity administers.
About 10 percent of participants increased the amount of money deferred from their paychecks during the quarter, McHugh said. That's up from 7.6 percent who increased in the first quarter of 2010.
A portion of the increase can be attributed to automatic escalation used by some companies in their 401(k) plans. The feature increases a worker's paycheck deduction automatically each year unless they opt out. Many of the automatic increases kick in during the first quarter.
When breaking the numbers down further, Fidelity found that workers who have saved continuously with the same employer for at least 10 years have amassed an average balance of $191,000. For the 10-year continuous contributor aged 55 or older, the average balance has reached $233,000.
Fidelity also has seen more workers seek help in making decisions about their retirement plans. Some use Internet tools or phone calls while others have attended workshops or one-on-one consultations.
"They're not just calling and checking their balances," McHugh said. "It's an understanding that they really need to take stock and understand what they need to do and take personal responsibility to make sure they're saving sufficiently."