Fidelity Investments, the nation's largest 401(k) administrator, said the average balance among its nearly 12 million accountholders was $74,600 at the end of March. That's up from $69,100 at the end of 2011.

Fidelity's 401(k) participants set aside an average $5,810 through paycheck deductions for the 12-month period ended March 31, and employers kicked an additional $3,360. Both numbers are slightly higher than they were a year ago.