https://techcrunch.com/2018/10/12/half-of-all-devices-now-run-ios-12/

Half of all devices are now running the latest version of the iOS mobile operating system, iOS 12, according to figures shared by Apple. On devices introduced in the last four years, that number is as high as 53 percent. And iOS 12 adoption is taking place more quickly than the last release did, Apple also notes.

As we previously reported, it took until November 6, 2017 for iOS 11 reach 52 percent of all current iPhones and iPads. iOS 12 achieved that milestone in mid-October.