To provide you with the best experience, after macOS 10.14 Mojave is made generally available in Fall 2018, the operating system (OS) requirement for Office for Mac is currently anticipated to change to support Apple’s three most recent versions of macOS. When macOS 10.14 is released, Office 365 for Mac and Office 2019 for Mac would support macOS 10.14, 10.13, and 10.12. Moving forward, as new major versions of macOS are made generally available, Microsoft would drop support for the oldest version and support the newest and previous two versions of macOS. For example, when the next version of macOS is released, Office for Mac would support the newest version as well as 10.14 and 10.13 while macOS 10.12 would no longer be supported.
What if I don't update macOS to a supported version?
If you’re on an unsupported version of macOS, your Office apps will still work but you would no longer receive any updates including security updates. For example, if you’re on macOS 10.12, but later you don’t update your macOS to a supported version when macOS 10.12 is no longer supported, you won’t receive any updates of any kind. As new major versions of macOS are released and older versions become unsupported, we highly recommend you continue to update your macOS to a supported version in order to receive mainstream support such as security updates as well as new features (if you’re an Office 365 for Mac subscriber). This applies for both Office 365 for Mac and Office 2019 for Mac users.
What about Office 2016 for Mac?
If you have a one-time purchase of Office 2016 for Mac or you have Office 365 for Mac and are using the Office 2016 for Mac build on macOS 10.11 or 10.10, your Office system requirements will not change.