After that, you're going to have to pay $119 to upgrade your PC to the latest and greatest Windows.
So, please, let me urge you, while there's time left: If you've been on the fence - if you're still running Windows 7 or especially Windows 8.1 - it's probably time to upgrade to Windows 10.
The last few weeks especially, Microsoft has been making headlines by using tactics to promote the Windows 10 upgrade that are annoying at best and misleadingly icky at worst. It's not a flattering look for Microsoft to push Windows 10 on people so aggressively, especially when there are plenty of good reasons to stay on older versions of Windows.
But if you can get past that ickiness, and if you don't have a pressing and immediate reason to stay on an older version, there are lots of great reasons to upgrade, and not a lot of reasons to hesitate.
First and foremost, Windows 10 is just plain nice to use. I, personally, have found lately that I can get more done on a Windows 10 machine like Microsoft's own Surface Book than on an Apple Macbook.
With Windows 10, Microsoft combined the best parts of Windows 7 (the Start menu, "snapping" Windows to the corners of the screen) and the best parts of Windows 8 (the touch-friendliness, and...that's pretty much it) to make something that's actually user-friendly across tablets and laptops alike.
Microsoft
Windows 10's Cortana.
Feature-wise, the Cortana digital assistant is like Apple's Siri, only more helpful - including ever-expanding capabilities to integrate with your calendar and help manage your time. If you have an Android phone, you'll soon be able to use Cortana to send and reply to texts from your computer, too.
And the new Xbox app in Windows 10 lets you stream gameplay from the Xbox One console straight to your PC or tablet. If you're console-less, the Xbox app is still super-handy for taking screenshots and videos from games and apps.
Under the hood, Microsoft also made some big changes that will pay dividends in the future: Windows 10 is the only place to get DirectX 12, the latest and greatest version of its long-lived graphics software. The best-looking PC games will require DirectX 12 sooner rather than later. And on that note, Windows 10 is getting a lot of great Xbox games, including a multiplayer-only version of Halo 5: Guardians.
Melia Robinson/Business Insider
Microsoft's Surface Book laptop is also a tablet.
Finally, Windows 10 has been billed as the most secure Windows ever. Indeed, the Department of Defense will be migrating 4 million employees to Windows 10 to take advantage of that security.
Really, there are a countless little things that make me like Windows 10. And there's a free "Anniversary Update" coming to Windows 10, likely not long after the free period is over, that will bring more little features and fixes.
I have a hunch you'll like Windows 10, too. So with the clock ticking, seriously, think about upgrading. You might just be glad you did it now, and not later when you don't get your free upgrade.