This page has details of when various versions of Windows fall out of Extended Support . N.B. These dates are simply when no new updates will be released for that version of Windows - it does not mean it will suddenly stop working after that date.
As time goes by hardware and software will not work on the older version of Windows - this is already the case for Microsoft Office 2013 and 2016, iTunes/Quicktime, Google Chrome, Opera, Kaspersky 2016 and McAfee Total Security. All these programs are no longer available for Windows earlier than 7.
Windows Vista users may be best advised to consider system replacements after April 2017 - this version of Windows was released back in 2006 and it is unlikely that a machine of this age will be best placed to cope with modern day programs even with a more modern operating system.
* The original version of Windows 8 is no longer supported - to continue receiving support and updates one must update to Windows 8.1.
** From Microsoft:
[Windows 10] updates are cumulative, with each update built upon all of the updates that preceded it. A device needs to install the latest update to remain supported. Updates may include new features, fixes (security and/or non-security), or a combination of both.https://support.microsoft.com/en-us/help/13853/windows-lifecycle-fact-sheet