For years now, mobile usability has been a factor in Google’s search algorithm. Sites that are optimized suitably for use on mobile devices rank higher than their non-optimized counterparts, even on desktop devices. But until now, that ranking factor has been both limited and ambiguous.
Aside from a “mobile-friendly” tag associated with various sites in mobile search results, it hasn’t been entirely clear which factors Google considers when calculating mobile rankings or how many sites (or which ones) are currently affected. Because of this, many business owners have postponed or avoided optimizing their sites for mobile devices, and have survived to tell about it.
Starting April 21, that’s all going to change.