Insider Preview builds of Windows 10 have a built-in “ticking 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 version of Windows 10 expires?

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

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

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

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

How to check the expiration date

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

This dialog shows you the exact expiration date and time for your version of Windows 10. You must update to a newer Insider build of Windows 10 (or downgrade to a previous stable version) before the expiration date.

The Winver dialog also shows you the precise version of Windows 10 that you are also using. This information can also be found in the Settings app.