https://arstechnica.com/gadgets/2019/01/windows-10-edges-past-windows-7-to-become-most-widely-used-windows/

About three and a half years after its release, Windows 10 seems to have convincingly passed Windows 7 in usage share. Online stat-tracking service Net Market Share puts Windows 10 at 39.22 percent of usage, versus 36.90 percent for Windows 7.

Web-based stat-tracking services vary in their estimates of who's using what operating system. That's due to different sites being monitored and different methodologies in handling the data. Net Market Share is the one we've seen most often quoted by third parties (including Microsoft and Mozilla), so it is notable as the companies' own preferred measure. Another widely referenced service, StatCounter, reckons that Windows 10 passed Windows 7 a year ago, putting the new operating system at 52.42 percent to its predecessor's 35.65 percent.