The figure is based on App Store tracking data as of Feb. 20, Apple said. The same data indicated that 16 percent of devices are on iOS 9, while 5 percent are relying on earlier operating systems.
That would so far suggest faster adoption than iOS 9, which by the same point last year was only on 77 percent of devices, having hit 75 percent in January. That in turn outpaced iOS 8, which took about six months to reach iOS 10's current levels.
As usual, Apple didn't indicate the reasons for iOS 10's performance. One is likely the record sales of the iPhone 7, which comes with iOS 10 pre-installed.
The software brought with it a number of changes, including Siri and Maps improvements, a dedicated Home app, an overhauled Messages with its own sub-apps, and an improved notification system, including media previews and inline message replies.
The combined featureset may have enticed a number of existing device owners to upgrade. Many of the people on previous iOS releases are presumably using devices deemed incompatible with iOS 10, such as 2011's iPhone 4s.
The next major version of iOS, iOS 11, should be shown off at this year's Worldwide Developers Conference, then go public sometime in the fall after a lengthy beta test.