Active stock fund managers around the world are holding the lowest percentage of Apple Inc (AAPL.O) shares in their portfolios when compared to the iPhone maker's overall weighting in indexes, even as the shares hit record highs, according to a research note by investment bank UBS late Monday.

The current positioning by investors suggests Apple stock has room to run as portfolio managers chase performance. This should give Apple more fuel even after it rallied 56.4 per cent in the 12 months leading up to Monday's close.

"Active fund managers as a whole continue to underperform their benchmarks and are not going to want to leave a lot of performance on the table if they continue to see this company rally," said Todd Rosenbluth, director of ETF and mutual fund research at CFRA, an independent research firm in New York.

Only about a third of large-cap core mutual funds are ahead of the 6.7 per cent gain in the benchmark S&P 500 index for the year to date, leaving portfolio managers struggling to prove their worth at a time when low-priced index funds and exchange traded funds that mimic benchmarks continue to take market share, Rosenbluth said.

The UBS ranking was based on institutional investment in individual stocks. The total dollar holdings in a stock were compared to the size of the overall fund portfolio to calculate the stock's "investor weight." This was later compared with "the relevant equity index benchmark to form the active weight."

For its part, global fund managers' "investor weight" of Apple stood at 1.3 per cent while their "active weight" positioning was negative 0.6 per cent, UBS data showed. In a regulatory filing, Warren Buffett's Berkshire Hathaway reported owning 57.4 million shares of Apple as of Dec. 31, up from just from 15.2 million shares three months earlier.

Shares of Apple are up about 26.8 per cent for the year to date in anticipation of a new iPhone model expected to be released in September marking the 10th anniversary of its flagship product.

Sales of the iPhone, which account for 69.4 per cent of Apple's total revenue, were larger than expected in the quarter that ended Dec. 31, helping mitigate concerns about consumers switching to cheaper alternatives or holding on to their current phones longer.

"You're not seeing a slowdown in demand ahead of a major upgrade year, and there's a potential for higher costs and margins with the new model," said Steve Chiavarone, a portfolio manager at Federated Investors.

Apple reports second-quarter results after the closing bell.