For the past five years, Apple's September iPhone-centric events have followed the same general formula. An event during the first week or two of the month, pre-orders shortly after, and then an official launch date approximately 10 days later. Apple's September schedule for 2012 to 2016 is below:

- iPhone 5 (2012) - Sept. 12 event, Sept.14 pre-orders, Sept. 21 launch.

- iPhone 5s (2013) - Sept. 10 event, no pre-orders, Sept. 10 launch.

- iPhone 6/6 Plus (2014) - Sept. 9 event, Sept. 12 pre-orders, Sept. 19 launch.

- iPhone 6s/6s Plus (2015) - Sept. 9 event, Sept. 12 pre-orders, Sept. 25 launch.

- iPhone 7/7 Plus (2016) - Sept. 7 event, Sept. 9 pre-orders, Sept. 16 launch.

If Apple plans to follow this same formula -- and it looks like that's what's happening -- pre-orders for the new "iPhone 8" and its companion devices the iPhone 7s and the iPhone 7s Plus will take place on Friday, September 15, MacRumors says.

Following pre-orders, the new devices will most likely see an official launch on Friday, September 22, with pre-order shipments going out to customers and in-store stock available.

Friday, September 15 is a highly logical guess as to when pre-orders will start, and unsurprisingly, that's the date being cited by German site Macerkopf. According to the site, German carriers are preparing for a September 15 pre-order date and a September 22 launch date.

While Apple tends to follow a specific September formula, there have been deviations. In 2013, for example, Apple did not accept pre-orders for the iPhone 5s due to supply constraints, and in 2015, pre-orders took place early on a Saturday morning. Still, September 15 and September 22 are the most likely dates for pre-orders and launch, respectively.