There was one option left which still allowed one to upgrade for free to Windows 10 from Windows 7 and Windows 8. While it can be termed to be mildly unethical one can use the Windows 10 free upgrade option for those who use assistive technologies. Many consider this option as a Microsoft’s way to allow more to jump on the Windows 10 bandwagon from Windows 7 and 8.
But now this option is also expiring on December 31.
Update: The page has been updated to mention that now this free upgrade offer expires on January 16. This is what the page which allows one to upgrade to Windows 10 for free reads,
If you use assistive technologies, you can upgrade to Windows 10 at no cost as Microsoft continues our efforts to improve the Windows 10 experience for people who use these technologies. Please take advantage of this offer before it expires on January 16, 2018.
So, unless Microsoft extends this offer you have the end of the year to use it and upgrade for free to Windows 10. As you know that Microsoft is doing away with the active support of older Windows versions one by one. With the increased threats from many Ransomware attacks seen in recent past, it is really wise to use this offer and upgrade to Windows 10 for keeping your PC supported.
You can follow this link to upgrade your PC to Windows 10 for free.