Our general policy is to support the current version minus one.
For example, at the time of writing, the current iOS version number is 11.2.1. The major version is 11, therefore we support iOS 10 and greater.
In some cases, depending on the timing of app updates, you may see current minus two (e.g. as of today, The Photographer's Transit still supports iOS 9, but that will change iOS 10 with the next update).
The rationale for this approach is
- Apple generally maintains hardware support for multiple iOS versions (e.g. you can still run iOS 11 on an iPhone 5S which was released in September 2013)
- There is a cost in terms of code complexity, testing and support when maintaining older iOS version support which comes at the expense of adding new and improved features
- The proportion of users unable to run the current minus one versions is extremely low
Thanks for your understanding.