Windows 7 can be use until 2020 and Windows 8 can be use until 2023
As we know, the 1 year free update to Windows 10 was ended on 29 July 2016 and various ways were took by Microsoft to make sure all the Windows users are update to latest version of Windows which is Windows 10. However, there are users that still don’t want to update to Windows 10 and try their best to continue using the older version of Windows and don’t want to update their machines to Windows 10 due to some reasons.
If you really don’t want to update your machine to Windows 10, You are be able to use the Windows 7 until 2020. This is because Microsoft are still supporting the Windows 7 until 14 January 2020 (End of Extended Support) although Microsoft was stopped to come out with new version of Windows 7 since 13 January 2015 (Mainstream Support Ends January 2015). After that, Microsoft will not give any security update to Windows 7. Same with Windows 7, the “Mainstream Support” for Windows 8 and Windows 8.1 will end on 9 January 2018 and the “Extended Support” will end on 10 January 2023.
Therefore, I will highly suggest you to update to the latest version of Windows before end of the Extended Support for the Windows 7, 8, and 8.1 as there are not any security update for those version of Windows to make sure the security of your computer system.