Average 401(k) balances at Fidelity Investments are at the highest they've been since the company started tracking the data 12 years ago, at $75,900 per account holder.

The figure is an 18% increase over a year ago. Fidelity's data is significant because the company is the nation's largest 401(k) provider, with 12 million accounts and more than 20,200 corporate plans.

Data also showed annual employee contributions have grown 7.3% over the past five years at the end of the third quarter, to $5,900, according to Fidelity. Average annual employer contributions are up an average of 19% over that time period, at $3,420.

"It's encouraging to see companies making a greater contribution to their employees' 401(k) plans as we know a healthy employer match not only impacts employees' retirement savings but also has a positive impact on their behavior, ultimately leading to better outcomes," said James M. MacDonald, president of workplace investing at Fidelity Investments. "And employers could do even more to help boost savings, such as increasing their default automatic enrollment rate and utilizing automatic annual increase programs that gradually raise an employee's savings rate."

--Raymond Fazzi