“According to IDC, Apple sold fewer Macs in the U.S. during the second quarter than it did in the same period a year earlier. If the research firm’s forecast is accurate, the decline would be Apple’s first in three years,” Gregg Keizer reports for Computerworld. “IDC estimated that Apple sold 1.81 million Macs in the U.S. during the quarter that ended June 30, down 1.1% from the 1.83 million machines sold in the same quarter of 2011.”

“Of course, there’s no guarantee that IDC’s estimate is on target. Ballparking Apple’s U.S. sales, said IDC analyst David Daoud, is a ‘very difficult exercise,'” Keizer reports. “Case in point: Gartner has a different take on Apple’s U.S. Mac sales. While it also put the Cupertino, Calif., company in the No. 3 slot on Thursday, behind both Hewlett-Packard and Dell, it set domestic sales at 1.91 million Macs for a 4.3% increase over the 1.83 million sold the year before.”

Keizer reports, “IDC said that HP’s sales were off 12% and Dell’s 9.2% for the quarter, while the overall U.S. PC business contracted by 10.6%. Gartner estimated HP and Dell were down — 12.7% and 9.5% — respectively, and that U.S. PC sales fell 5.5%. So even if IDC’s more pessimistic prognostication proves correct, Apple will be able to boast that it beat the PC average for another quarter. Another positive in both IDC’s and Gartner’s forecasts of Thursday: Because of the large sales decline overall, Apple gained ground in U.S. market share. IDC said Apple’s share of U.S. sales for the quarter climbed to 11.4%, up over a percentage point, while Gartner had Apple accounting for 12% of all personal computer sales during the period.”

Read more in the full article here.

MacDailyNews Note: Apple does not report U.S. Mac unit sales, just total worldwide Mac unit sales each quarter. Unless an Apple executive specifically states U.S. Mac unit sales in a conference call or elsewhere, there is simply no way to tell if Gartner or IDC are ever correct with their estimates, but their estimates do differ from each other, sometimes rather widely:

Gartner vs. IDC: U.S. Mac unit sales estimates, Q111-Q112, MacDailyNews.com

Here’s the same data with Apple’s actual worldwide Mac unit sales alongside:

Gartner vs. IDC: U.S. Mac unit sales estimates and Apple worldwide actual Mac unit sales, Q111-Q112, MacDailyNews.com