Retirement account balances, which fell at the start of the year due to market volatility, bounced back in the second quarter, according to the latest data from Fidelity Investments, the nation's largest provider of 401(k) savings plans.

The average 401(k) balance jumped 8% from a year earlier to $137,800, a record high, Fidelity found .

The average individual retirement account balance also rose 5% year over year to $131,366.

Number of 401(k), IRA millionaires hit all-time highs

The rebound in account balances helped boost the number of 401(k) millionaires to an all-time high.

The number of 401(k) accounts with a balance of $1 million or more jumped to 595,000 as of June 30, up 16% from the first quarter, according to Fidelity.

The number of IRA-created millionaires

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