Apple represents 3.1 percent of the S&P 500, second only to Irving, Texas-based Exxon Mobil Corp., which has a weighting of 3.3 percent. Danoff's Contrafund had 6.8 percent of its assets in Apple, owning 16 million shares as of June 30, making it the largest mutual fund holder of the stock. Apple accounted for 13 percent of the fund's gains since Jan. 20, 2009, according to Bloomberg calculations.

The other funds among the 10 biggest holders that got at least that much help from Apple were the $17.7 billion Fidelity Advisor New Insights Fund (13 percent), the $7.8 billion Fidelity OTC Portfolio (14 percent), the $26.7 billion T. Rowe Price Growth Stock Fund (15 percent), the $8.7 billion Janus Twenty Fund (28 percent) and the $5.5 billion Janus Forty Fund (23 percent).

Beating the Index

Bloomberg portfolio analysis allows measuring how much an individual stock contributes to a mutual fund's performance over any given period of time. Because the fund data is gathered on either a monthly or quarterly basis, the calculation is approximate, not precise. The analysis cannot be done on mutual funds that own both stocks and bonds.

While it has helped performance, owning Apple is no guarantee a fund will outperform peers. The two Janus funds equaled approximately the 69 percent return in the S&P 500 between Jan. 20, 2009, and Aug. 1, 2011.

The other four funds did better, with T. Rowe Price Growth returning 89 percent and Fidelity OTC gaining 126 percent. The two funds managed by Danoff, Fidelity Contrafund and Fidelity Advisor New Insights, rose 74 percent and 72 percent, respectively.

Janus Twenty

Janus Twenty, which had the largest contribution to performance from Apple, fared the worst, rising 68 percent.

"The past two years have been miserable for this fund," Kathryn Young, an analyst at Morningstar, wrote in a July note. Young said the poor showing was a reflection of losses in holdings such as Bank of America Corp. and San Jose, California- based Cisco Systems Inc.

Charlotte, North Carolina-based Bank of America fell 29 percent this year; Cisco dropped 24 percent. Janus Twenty sold both holdings as of June 30, Bloomberg data show.

The fund, run by Ron Sachs, 44, is a concentrated portfolio that typically holds 20 to 30 stocks, according to the website of Denver, Colorado-based Janus Capital Group Inc. Sachs wasn't available to comment because Janus managers do not discuss individual stocks, James Aber, a spokesman for the company, wrote in an e-mail.

The fund cut its holdings of Apple shares by more than 50 percent between Oct. 31, 2009, and March 31, 2011, regulatory filings show.