It's likely a lot of users held off upgrading until Apple had sorted out the bugs.
43 per cent of Apple users are on iOS 7, while 5 per cent use an earlier version.
Google has promised to rectify this with Android Lollipop, which is due to launch imminently.
iOS 8 has had its fair share of issues. Users have complained that Bluetooth, Wi-Fi and mobile network access have all struggled to connect.
iOS 8.1 also adds new features to Continuity, which lets your Apple devices work together seamlessly. You can reply to a text message and take calls from your iMac, for example.
Apple Pay has been a big hit so far in the US, with 1 million bank cards registered in the first three days. Some US retailers have refused to allow it, however, as they're preparing their own mobile payment system.