Come to find out, the end of support date has been known since before the release of date of Windows 10 (July 29, 2015). From
Support for Windows 10 Will Last Until 2025, published July 20, 2015:
Microsoft today said that its next OS release will have official support for the customary 10 years.
An update on the company's Windows lifecycle fact sheet Web site showed that official extended support for Windows 10 will end on Oct. 14, 2025 and mainstream support will conclude five years earlier on Oct. 13, 2020.