With over 800 million PCs running Windows 10, Microsoft’s Windows 10 is the world’s most popular computer operating system. It’s also the last version of Windows operating system as Microsoft will update Windows 10 (for free) rather than releasing a new version of Windows. Most of the home users have upgraded to Windows 10 using the free Windows 7/8/8.1 upgrade offer that Microsoft had started along with the release of Windows 10. In fact, even today, PC users with genuine copies of Windows 7/8/8.1 are allowed to upgrade to Windows 10 for free although Microsoft has officially stopped the free upgrade program about a year ago. One can also use genuine Windows 7/8 product key to activate Windows 10. How long can you use Windows 10 without activation? Well, we cannot say for how many days one can use Windows 10 without activation as Windows 10 seems to work without activation for years. Since inactivated Windows 10 install doesn’t stop working or booting up after x number of days, it’s hard to tell how long one can use Windows 10 without activation. That said, if you would like to run Windows 10 without any annoying messages and want to have access to all its settings, you need to activate Windows 10 from day one only. Can I use Windows 10 without activation? Windows 10 displays “Activate Windows. Go to settings to activate Windows” watermark at the lower right corner of the desktop when running Windows 10 without activation. When you are running an unlicensed copy of Windows 10, you will get “Windows isn’t activated. Activate Windows now” message at the home page of the Settings app. You will get “You need to activate Windows before you can personalize your PC” message on all pages under the Personalization category. When it comes to functionality, you won’t be able to personalize the desktop background, window title bar, taskbar, and Start color, change the theme, customize Start, taskbar, and lock screen. However, you can set a new desktop background from the File Explorer without activating Windows 10. The Settings > Update & Security > Activation page also displays the “Windows is not activated” message if your Windows 10 is not activated. Additionally, you might periodically get messages asking to activate your copy of Windows 10. This might annoy you as the message might show up in the middle of your work. The biggest issue with an unlicensed copy of Windows 10 probably is not being able to personalize Windows 10. All other features will work just like on a licensed copy of Windows 10. So being not able to personalize and that nagging watermark are the main (only?) issues when using Windows 10 without activation. We here at IntoWindows strongly recommend you activate your copy of Windows 10 right away by buying a legit/genuine copy of Windows 10 either from Microsoft Store online or from a retail shop. How to check if your Windows 10 activated? Checking your Windows 10 activation status is easy. Navigate to Settings app > Update & Security > Activation page to know the current activation status of Windows 10 installation. If it’s activated, don’t forget to link Windows 10 license to your Microsoft account to avoid activation issues if and when you change your PC’s hardware. You can also use the official Windows 10 activation troubleshooter to fix Windows 10 activation issues. How to activate Windows 10? Step 1: Navigate to Settings > Update & security > Activation page. Step 2: In the Activate Windows now section, click the Change product key link, type the product key, and then click the Next button to activate your copy of Windows 10. Please note that your PC must be connected to a working internet connection in order to activate Windows 10.