(CNN/Money) The surging stock market helped boost average 401(k) balances to yet another record high in 2013. But many young and low-income workers are not doing such a great job of keeping that cash in their accounts.

The average 401(k) balance hit $89,300 at the end of the year, up 15.5% from $77,300 in 2012, according to an annual tally by Fidelity Investments. Most of the boost came from stock market gains as all three major stock indexes ended the year more than 20% higher.

People on the verge of retirement, ages 55 to 64 years old, saw their nest eggs grow to an average balance of $165,200 from $143,300 in 2012, Fidelity said. Savers with both a 401(k) plan and Individual Retirement Account managed by Fidelity had larger nest eggs, with an average balance of $261,400, up from $225,600 in 2012.

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