Insider Preview builds of Windows 10 have a built-in “time bomb.” Each comes with an expiration date, and Windows will eventually refuse to boot entirely after that date. Here’s how to check when that will happen.

What Happens When a Windows 10 Build Expires?

This only applies to unstable Insider Preview versions of Windows 10. Stable versions of Windows 10 will never “expire” and stop working, even when Microsoft stops updating them with security patches.

When a build of Windows 10 expires, Microsoft says you will see a warning that you’re using an expired build. The warning will reappear once per day, and you will also see UAC (User Access Control) warnings. Previous reports have said that Windows 10 will reboot every three hours after it expires, so Microsoft may have made the expiration process less annoying.

In the past, Microsoft has said that expired builds will no longer boot two weeks after the expiration date. You’ll need to reinstall a newer build of Windows—or an older stable build that won’t expire—to use your PC once again.

Microsoft expires these builds to prevent people from staying with old, unstable versions of Windows 10. These builds of Windows 10 are made available for testing, and there’s no point in testing an old build that has a bunch of already-fixed bugs.

How to Check the Expiration Date

You can check the expiration date from the winver application. To open it, press the Windows key, type “winver” into the Start menu, and press Enter. You can also press Windows+R to open the Run dialog, type “winver” into it, and press Enter.

This dialog shows you the precise expiry date and time for your build of Windows 10. You should update to a newer Insider build of Windows 10 (or go back to a previous stable build) before the expiration date.

The winver dialog also shows you the precise Windows 10 build you’re using, too. This information can also be found in the Settings app.

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