It is a well-known fact, that it is possible to extend the initial grace period for activating your (hopefully legitimate!) copy of Windows from 30 days to 120 days by using slmgr. This is a tool that is intended to allow the preparation of image-based installers for enterprise use by allowing to reset the initial grace period up to 3 times.
If you tend to forget the number of times you already reset the counter, you can easily check for yourself: simply run
slmgr -dlv
to get detailed licensing information, including the number of remaining re-arms and remaining grace time.
If you want to know when exactly your grace period runs out, use
slmgr -xpr
Note: This simply gives you more time, it won’t prevent you from having to buy and/or activate Windows. Re-arming is not a bug, it works as intended and is an important tool for use in corporate environments.