Watch time

YouTube learned in 2011 that a click did not mean a video was actually watched ¹, so in 2012 it added watch time, which videos someone watched and for how long, to its recommendations ². Views dropped 20% right after the change ³. That October it also began ranking search to reward videos that keep viewers watching ⁴. YouTube later added surveys because, in its words, not all watch time is equal ⁵. More in YouTube recommendations.

TikTok gives finishing a longer video from beginning to end as its example of a strong indicator of interest, weighted above weak ones ¹. Instagram says its most important Reels predictions include how likely you are to watch a reel all the way through ², and in Feed it predicts how likely you are to spend a few seconds on a post ³. See TikTok For You feed, Instagram Reels and Instagram ranking.

YouTube defines average view duration as the average minutes watched per view ¹ and watch time as the amount of time viewers have watched ², so total watch time is average view duration times views. A retention curve shows who is still watching at each moment; a flat line means viewers watch that part from start to finish ³. Its intro metric is the share still watching after the first 30 seconds ⁴. Same curve, different length: a 10-minute video earns 40 times the watch time of a 15-second one.