July 21 (Bloomberg) -- Apple Inc. reported a 31 percent increase in third-quarter profit on sales of its Macintosh personal computer. The shares fell after the company forecast revenue and earnings that missed analysts' estimates.

Net income climbed to $1.07 billion, or $1.19 a share, from $818 million, or 92 cents, a year earlier, Cupertino, California- based Apple said today in a statement. Apple predicted a fourth- quarter profit of $1 a share and sales of $7.8 billion, below the $1.24 a share in profit and $8.3 billion in sales anticipated by analysts in a Bloomberg survey.

The forecast raises concern that Chief Executive Officer Steve Jobs may not get as big a boost from back-to-school shopping and sales of its new iPhone 3G this quarter. After record Mac orders last quarter, investors had expected Apple to build on those sales in the current period.

The low forecast ``is something they do every quarter,'' Andy Hargreaves, an analyst at Pacific Crest Securities, said in an interview from Portland, Oregon. ``It shouldn't surprise people, but it does.''

Apple typically beats its own projections and has topped analysts' estimates for sales and profit in the past eight quarters.

Apple fell $8.63, or 5.2 percent, to $157.66 in late trading after closing at $166.29 at on the Nasdaq Stock Market. The shares have dropped 16 percent this year.

Third-quarter sales rose 38 percent to $7.46 billion, topping analysts' estimates of $7.36 billion. Apple sold a record 2.5 million Macs, wooing buyers with models such as the ultra- slim Air notebook. Analysts had estimated profit of $1.08 a share in the period, which ended June 28.

IPhone Lull

Apple, which introduced the original iPhone in June 2007, ran out of inventory in May as it prepared a new version of the wireless device. The company opted to delay recording sales from phones sold last quarter until it released a software upgrade.

That update accompanied the introduction of Apple's new iPhone 3G in 21 countries on July 11. The software, which also works with older iPhones, adds support for corporate e-mail and third-party programs. Since the new phone debuted after the quarter ended, it also wasn't included in today's results.

Shoppers bought 1 million iPhones in the device's first three days, Jobs said. Apple's partners in the U.S., U.K., Germany, Canada and Japan reported that many shops ran out on the first day.

Third Place

Apple's PC market share rose to 8.5 percent in the U.S. last quarter, from 6.4 percent a year ago, said Stamford, Connecticut- based Gartner Inc. The Mac accounts for about half of the company's sales. Dell Inc. and Hewlett-Packard Co., which both sell Windows-based PCs, lead the U.S. market.

Every extra point of PC market share adds $6 billion to Apple's sales and $1 a share to earnings, according to Kathryn Huberty, an analyst at Morgan Stanley in New York.

Both Mac and iPod sales may have benefited from a tax rebate intended to stimulate the economy, said Toni Sacconaghi, an analyst at Sanford C. Bernstein & Co. in New York. He cited reports from U.S. retailers that saw a rise in spending after more than 130 million U.S. households received checks.

This quarter, analysts and investors expect back-to-school demand to fuel Mac sales. Broader distribution of the iPhone also will stoke revenue. The iPhone 3G is now available in four times as many countries, and Jobs plans to bring it to a total of 70 nations in coming months.

The company said it sold 11 million iPod media players and 717,000 iPhones in the third quarter. On average, analysts were projecting sales of 10.3 million iPods, 2.2 million Macs and at least 700,000 iPhones, said Gene Munster at Piper Jaffray & Co. in Minneapolis.

To contact the reporter on this story: Connie Guglielmo in San Francisco at cguglielmo1@bloomberg.net

Last Updated: July 21, 2008 17:00 EDT