Mozcast features report is now showing that 50% of the Google's search results that come up are now listed as HTTPS. Just last October, that figure hit 40% and in January 2016, it was only 25%.
Here is the Mozcast chart:
Of course, most of this is because Google really has pushed hard to encourage webmasters and service providers to go HTTPS.
The interesting thing is only Google really knows the real percentage because a tool like RankRanger for their tracking set shows almost 98%. Well, 98% seems unrealistic. With RankRanger, they are tracking that 98% of page one SERPs have at least 1 HTTPS result, not that 98% of all results are HTTPS
Forum discussion at Twitter.