Fidelity Investments said Thursday that the average balance for its customers’ 401(k) retirement accounts has returned to September 2008 levels.

The average balance rose nearly 13 percent to $60,700 at the end of the third quarter from the end of the previous quarter, and increased 28 percent from the end of the first quarter low of $47,500. The average balance was $58,400 at the end of the third quarter of 2008.

Fidelity attributed the rise to the rally in the equity markets — the Standard & Poor’s 500-stock index had a total return of 34 percent over the second and third quarter combined — as well as employee contributions and the reinstatement of employer matching programs as the economy began to recover.

The analysis was based on the accounts of more than 11 million participants in the more than 17,000 corporate defined-contribution plans at Fidelity.