Rene Ritchie, iMore:

Since iPhone 5, Apple has announced every new iPhone during a special event held the first or second Tuesday or Wednesday of September.

Rene lays out the dates of Apple’s September events since 2013 and makes his best guess:

It’s likely we’ll see this year’s event on or around Wednesday, September 12.

And this from John Gruber:

I have no inside information on this, but September 12 is definitely my guess, for all the same reasons Ritchie mentions. Since moving iPhone intro events to September in 2012 with the iPhone 5, they’ve had three events on Tuesdays and three on Wednesdays. For whatever reason, I don’t think they like Thursdays.

I do love this game, for some reason. Part of it, for me, is that this kind of guessing hurts no one and does stoke the embers for the event without revealing something that would diminish the event.

September 12th sounds good to me.