401(k) balances grow, but savings is still not enough

At Fidelity, the average 401(k) balance hit $91,300 by the end of 2014. While that's up just 2% from 2013, it's a jump of more than 30% from 2011's average balance of $69,100, Fidelity reported.

Average 401k balances 2014

The increase was due in part to the stock market, which saw the S&P 500 climb by more than 10%-- its third year of double-digit gains. But a spike in worker contributions also played a significant role.

Workers and their employers contributed an average of $9,670 in 2014, up 4% from the year before.

On average, employees socked away 8.1% of their salary, the highest savings rate recorded by Fidelity since 2011. Including an employer match, workers saved around 12% of their salary.

Consistent savers are doing especially well. Savers in their 401(k) plan for 10 years or more had an average balance of $248,000 -- an increase of 11% from what similar savers had a year ago.

The bad news: most people will need far more than that for a comfortable retirement. The common 4% rule for example, dictates that $250,000 would provide only $10,000 a year in retirement income.