Source: http://www.bruceclay.com/blog/mobile-friendly-seo-ranking/
The mobile-friendly algorithm update that was rolled out by Google last April 2015 was sort of a bust. While this update spurred many site owners to make their websites better for smartphone users, there was not a lot of movement across mobile search engine results page especially at the top of SERPs.
However, Google has just announced another mobile ranking boost and says that there will be an increase of effect of the mobile friendly ranking signal in May of this year.
“Today we’re announcing that beginning in May, we’ll start rolling out an update to mobile search results that increases the effect of the ranking signal to help our users find even more pages that are relevant and mobile-friendly.”
And a later clarification: “If you’ve already made your site mobile-friendly, you will not be impacted by this update.”
As of the moment, it seems that the mobile-friendly status as well as the resulting ranking increase is still a binary consideration. We will have to wait and see whether this latest change will start to shuffle the rankings more dramatically.