Analyst: Sept. 12 launch adds 6-10M iPhone 5s to Apple’s Q4

August 15, 2012, 10:05 AM UTC

Source: Piper Jaffray. Click to enlarge.

FORTUNE — With all the talk of a new iPhone launch in September — rather than October, as previously rumored — I had expected to see the Apple (AAPL) analysts rushing to adjust their models accordingly.

After all, any iPhone sales made on or before Sept. 29 — the last day of Apple’s fourth fiscal quarter of 2012 — would get counted as revenue in a quarter that all of Wall Street expected to be another disappointment.

Finally on Wednesday Piper Jaffray’s Gene Munster addressed the issue. He still hasn’t updated his model — and neither, he says, have the other Apple analysts — but he did do the math. (See spreadsheet, above.)

“We believe,” he wrote in a note to clients, “that a September launch could result in the final 10 days of the month generating 6-10 million iPhone 5 unit sales, which would likely shift out of December. We believe if iPhone 5 launches in September, Apple could sell 26-28 million units in the quarter (this takes into account iPhone sales slowing dramatically from September 12-20, which is announcement to availability). This would imply 8% upside to the Street’s current $35 billion in revenue and 12% upside to EPS of $8.46.”

The Street is currently expecting Apple to sell 23 million iPhones in Q4, not 27.19 million.

To complete his calculation, Munster writes, he would have to reduce his estimate of iPhone sales in the December quarter (fiscal Q1 2013), currently at 49 million.

But it all evens out in the end, he says:

“While predicting the timing of the iPhone release is topical for investors, we continue to believe that whether iPhone 5 launches in the September or December quarter is largely irrelevant to the overall story, which we believe is that the new phone will be the largest consumer electronics product upgrade in history.”